🕷️ Crawler Inspector

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Raw Queries and Responses

1. Shard Calculation

Query:

Response:

Calculated Shard: 62 (from laksa041)

2. Crawled Status Check

Query:

curl -X POST \
  'http://laksa062.int.ahrefs:8124/' \
  -H 'Content-Type: text/plain' \
  -H 'X-ClickHouse-Database: crawler3' \
  -H 'Authorization: Basic YXBpOg==' \
  -d 'SELECT getAhrefsURLFromUnparsed(src_unparsed) AS found_url, ifNull(toUnixTimestamp(download_stamp), 0) AS crawl_time, ifNull(toUnixTimestamp(props_url_first_seen), 0) AS first_indexed_time, download_http_code AS http_code, src_unparsed AS src_unparsed, src_root_hash AS src_root_hash, history_drop_reason AS history_drop_reason, meta_title AS meta_title, meta_descriptions AS meta_descriptions, attrs_boilerpipe_text AS attrs_boilerpipe_text, attrs_markdown AS attrs_markdown, attrs_readable_markdown AS attrs_readable_markdown, meta_canonical AS meta_canonical FROM crawler3.page_info_local FINAL PREWHERE (src_root_hash, src_unparsed) IN ((getAhrefsRootHashFromUnparsed(getAhrefsUnparsedNoserviceFromURL(\'https://www.britannica.com/event/Deepwater-Horizon-oil-spill\')), getAhrefsUnparsedNoserviceFromURL(\'https://www.britannica.com/event/Deepwater-Horizon-oil-spill\'))) FORMAT JSONEachRow'

Response:

{"found_url":"https:\/\/www.britannica.com\/event\/Deepwater-Horizon-oil-spill","crawl_time":1776348664,"first_indexed_time":1553938295,"http_code":200,"src_unparsed":"com,britannica!www,\/event\/Deepwater-Horizon-oil-spill s443","src_root_hash":"5455945239613777662","history_drop_reason":null,"meta_title":"Deepwater Horizon oil spill | Summary, Effects, Cause, Clean Up, & Facts | Britannica","meta_descriptions":["Deepwater Horizon oil spill, largest marine oil spill in history, caused by an April 20, 2010, explosion on the Deepwater Horizon oil rig—located in the Gulf of Mexico, approximately 41 miles (66 km) off the coast of Louisiana—and its subsequent sinking on April 22."],"attrs_boilerpipe_text":"Top Questions\nWhen did the Deepwater Horizon oil spill happen?\nWho owned the rig responsible for the Deepwater Horizon oil spill?\nWhat caused the Deepwater Horizon oil spill?\nHow did the Deepwater Horizon oil spill affect birds?\nDeepwater Horizon oil spill\n,  largest marine\noil spill\nin history, caused by an April 20, 2010, explosion on the\nDeepwater Horizon\noil rig—located in the\nGulf of Mexico\n, approximately 41 miles (66 km) off the coast of\nLouisiana\n—and its\nsubsequent\nsinking on April 22.\nThe explosion\nObserve fireboat responding to crews battling the fire during the Deepwater Horizon oil spill of 2010\nFireboat response crews battling the blazing remnants of the offshore oil rig Deepwater Horizon in the Gulf of Mexico, April 21, 2010.\nSee all videos for this article\nThe Deepwater Horizon rig, owned and operated by offshore-oil-drilling company\nTransocean and leased by\noil\ncompany\nBP\n, was situated in the Macondo oil prospect in the Mississippi Canyon, a valley in the\ncontinental shelf\n. The oil well over which it was positioned was located on the seabed 4,993 feet (1,522 metres) below the surface and extended approximately 18,000 feet (5,486 metres) into the\nrock\n. On the night of April 20 a surge of\nnatural gas\nblasted through a\nconcrete\ncore recently installed by contractor\nHalliburton\nin order to seal the well for later use. It later emerged through documents released by\nWikileaks\nthat a similar incident had occurred on a BP-owned\nrig\nin the\nCaspian Sea\nin September 2008. Both cores were likely too weak to withstand the pressure because they were composed of a\nconcrete\nmixture that used\nnitrogen\ngas to accelerate curing.\nOnce released by the fracture of the core, the\nnatural gas\ntraveled up the Deepwater rig’s riser to the platform, where it ignited, killing 11 workers and injuring 17. The rig capsized and sank on the morning of April 22, rupturing the riser, through which\ndrilling mud\nhad been injected in order to counteract the upward\npressure\nof oil and natural gas. Without any opposing\nforce\n, oil began to\ndischarge\ninto the gulf. The volume of oil escaping the damaged well—originally estimated by BP to be about 1,000 barrels per day—was thought by U.S.\ngovernment\nofficials to have peaked at more than 60,000 barrels per day.\nLeaking oil\nAlthough\nBP\nattempted to activate the rig’s\nblowout preventer (BOP), a fail-safe mechanism designed to close the channel through which oil was drawn, the device malfunctioned.\nForensic\nanalysis of the BOP completed the following year determined that a set of massive blades known as blind shear rams—designed to slice through the pipe carrying oil—had malfunctioned because the pipe had bent under the pressure of the rising gas and oil. (A 2014 report by the U.S. Chemical Safety Board claimed that the blind shear rams had activated sooner than previously thought and may have actually punctured the pipe.)\nEfforts in May to place a\ncontainment dome over the largest leak in the broken riser were thwarted by the buoyant action of gas\nhydrates\n—gas molecules in an ice matrix—formed by the reaction of natural gas and cold water. When an attempt to employ a “\ntop kill,” whereby\ndrilling mud\nwas pumped into the well to stanch the flow of oil, also failed, BP in early June turned to an apparatus called the\nLower Marine Riser Package (LMRP) cap. With the damaged riser shorn from the LMRP—the top segment of the BOP—the cap was lowered into place. Though fitted loosely over the BOP and allowing some oil to escape, the cap enabled BP to\nsiphon\napproximately 15,000 barrels of oil per day to a\ntanker\n. The addition of an\nancillary\ncollection system\ncomprising\nseveral devices, also tapped into the BOP, increased the collection rate to approximately 25,000 barrels of oil a day.\nBritannica Quiz\nDisasters of Historic Proportion\nIn early July the LMRP cap was removed for several days so that a more permanent seal could be installed; this capping stack was in place by July 12. Though the leak had slowed, it was estimated by a government-commissioned panel of scientists that 4,900,000 barrels of oil had already leaked into the gulf. Only about 800,000 barrels had been captured. On August 3 BP conducted a “\nstatic kill,” a procedure in which drilling mud was pumped into the well through the\nBOP\n. Though similar to the failed top kill, mud could be injected at much lower pressures during the static kill because of the stabilizing influence of the capping stack. The defective BOP and the capping stack were removed in early September and replaced by a functioning BOP.\nThe success of these procedures cleared the way for a “\nbottom kill,” considered to be the most likely means of permanently sealing the leak. This entailed pumping\ncement\nthrough a channel—known as a\nrelief well—that paralleled and eventually intersected the original well. Construction of two such wells had begun in May. On September 17 the bottom kill maneuver was successfully executed through the first relief well. The second had been intended to serve as a\nbackup\nand was not completed. Two days later, following a series of pressure tests, it was announced that the well was completely sealed.\nQuick Facts\nAlso called:\nGulf of Mexico oil spill\nDate:\nApril 20, 2010 - September 19, 2010\n(Anniversary in 4 days)\nTrusted knowledge for those who want to know more.\nSUBSCRIBE\nClaims by several research groups that subsurface plumes of dispersed\nhydrocarbons\nhad been detected in May were initially dismissed by BP and the\nNational Oceanic and Atmospheric Administration\n(NOAA). However, it was verified in June that the plumes were in fact from the Deepwater spill. The effect of the microscopic oil droplets on the ecosystem was unknown, though their presence, along with that of a layer of oil several inches thick discovered on portions of the seafloor in September, cast doubt on earlier\npredictions\nabout the speed with which the discharged oil would dissipate.\nBacteria\nthat had adapted to consuming naturally occurring gas and oil seeping from the seabed were thought to have consumed a portion of it.","attrs_markdown":"[![Encyclopedia Britannica](https:\/\/cdn.britannica.com\/mendel\/eb-logo\/MendelNewThistleLogo.png)](https:\/\/www.britannica.com\/)\n\n[![Encyclopedia 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Chatbot](https:\/\/www.britannica.com\/chatbot)\n\n[Games & Quizzes](https:\/\/www.britannica.com\/quiz\/browse)  [History & Society](https:\/\/www.britannica.com\/History-Society)  [Science & Tech](https:\/\/www.britannica.com\/Science-Tech)  [Biographies](https:\/\/www.britannica.com\/Biographies)  [Animals & Nature](https:\/\/www.britannica.com\/Animals-Nature)  [Geography & Travel](https:\/\/www.britannica.com\/Geography-Travel)  [Arts & Culture](https:\/\/www.britannica.com\/Arts-Culture)  [ProCon](https:\/\/www.britannica.com\/procon)  [Money](https:\/\/www.britannica.com\/money)  [Videos](https:\/\/www.britannica.com\/videos)\n\n[Deepwater Horizon oil spill](https:\/\/www.britannica.com\/event\/Deepwater-Horizon-oil-spill)\n\n- [Introduction & Top Questions](https:\/\/www.britannica.com\/event\/Deepwater-Horizon-oil-spill)\n- [The explosion](https:\/\/www.britannica.com\/event\/Deepwater-Horizon-oil-spill#ref294125)\n- [Leaking oil](https:\/\/www.britannica.com\/event\/Deepwater-Horizon-oil-spill#ref294126)\n- [Cleanup efforts](https:\/\/www.britannica.com\/event\/Deepwater-Horizon-oil-spill\/Cleanup-efforts)\n- [Aftermath and impact](https:\/\/www.britannica.com\/event\/Deepwater-Horizon-oil-spill\/Cleanup-efforts#ref294127)\n- [Legal action](https:\/\/www.britannica.com\/event\/Deepwater-Horizon-oil-spill\/Legal-action)\n  - [Charges, settlements, and penalties](https:\/\/www.britannica.com\/event\/Deepwater-Horizon-oil-spill\/Legal-action#ref334021)\n  \n  - [Charges against individuals](https:\/\/www.britannica.com\/event\/Deepwater-Horizon-oil-spill\/Legal-action#ref334022)\n  \n  - [The civil trial](https:\/\/www.britannica.com\/event\/Deepwater-Horizon-oil-spill\/Legal-action#ref334023)\n- [Environmental costs](https:\/\/www.britannica.com\/event\/Deepwater-Horizon-oil-spill\/Environmental-costs)\n- [The Deepwater Horizon oil spill in pictures](https:\/\/www.britannica.com\/event\/Deepwater-Horizon-oil-spill\/Environmental-costs#ref294128)\n\n[References & Edit History](https:\/\/www.britannica.com\/event\/Deepwater-Horizon-oil-spill\/additional-info)  [Quick Facts & Related Topics](https:\/\/www.britannica.com\/facts\/Deepwater-Horizon-oil-spill)\n\n[Images & Videos](https:\/\/www.britannica.com\/event\/Deepwater-Horizon-oil-spill\/images-videos)\n\n[![Deepwater Horizon oil rig: fire](https:\/\/cdn.britannica.com\/58\/139558-004-2F1526EA\/Fireboat-response-crews-blaze-oil-rig-Deepwater-April-21-2010.jpg)](https:\/\/cdn.britannica.com\/58\/139558-050-9EEE9E93\/Fireboat-response-crews-blaze-oil-rig-Deepwater-April-21-2010.jpg)   [![Deepwater Horizon oil spill: debris and oil](https:\/\/cdn.britannica.com\/59\/139559-004-71A72F92\/Debris-oil-rig-Deepwater-Horizon-April-22-2010.jpg)](https:\/\/cdn.britannica.com\/59\/139559-050-B9437E07\/Debris-oil-rig-Deepwater-Horizon-April-22-2010.jpg)\n\n[![Observe fireboat responding to crews battling the fire during the Deepwater Horizon oil spill of 2010](https:\/\/cdn.britannica.com\/35\/139435-138-1AC5B657\/Fireboat-response-crews-remnants-offshore-oil-rig-April-21-2010.jpg?w=400&h=225&c=crop)](https:\/\/www.britannica.com\/video\/Fireboat-response-crews-remnants-offshore-oil-rig-April-21-2010\/-142250)\n\n[![Deepwater Horizon oil spill of 2010: path of the oil](https:\/\/cdn.britannica.com\/13\/144913-004-DF74E60F\/Map-oil-spill-effects-Deepwater-Horizon-explosion-April-20-2010.jpg)](https:\/\/cdn.britannica.com\/13\/144913-050-B931EC84\/Map-oil-spill-effects-Deepwater-Horizon-explosion-April-20-2010.jpg)\n\n[![See how wire entanglement inside a well bore mitigates the effects of blowout preventer failure in an oil well](https:\/\/cdn.britannica.com\/77\/186377-138-E57058AA\/use-obstruction-wire-effects-oil-well-blowout.jpg?w=400&h=225&c=crop)](https:\/\/www.britannica.com\/video\/use-obstruction-wire-effects-oil-well-blowout\/-204448)\n\n[![Deepwater Horizon oil spill: controlled burn](https:\/\/cdn.britannica.com\/49\/141349-004-B78DD4D8\/oil-burn-disaster-Deepwater-Horizon-Gulf-of-May-6-2010.jpg)](https:\/\/cdn.britannica.com\/49\/141349-050-4E645470\/oil-burn-disaster-Deepwater-Horizon-Gulf-of-May-6-2010.jpg)   [![Deepwater Horizon oil spill: beach cleanup](https:\/\/cdn.britannica.com\/32\/142532-004-915959E6\/Workers-beach-oil-BP-Port-Fourchon-Louisiana-May-23-2010.jpg)](https:\/\/cdn.britannica.com\/32\/142532-050-827D3EE3\/Workers-beach-oil-BP-Port-Fourchon-Louisiana-May-23-2010.jpg)   [![Deepwater Horizon oil spill: avian casualty](https:\/\/cdn.britannica.com\/52\/141352-004-39C60C27\/bird-oil-spill-Gulf-of-Mexico-Deepwater-June-2010.jpg)](https:\/\/cdn.britannica.com\/52\/141352-050-41B2F42A\/bird-oil-spill-Gulf-of-Mexico-Deepwater-June-2010.jpg)   [![Deepwater Horizon oil spill: skimming](https:\/\/cdn.britannica.com\/28\/142528-004-3BC77414\/oil-coast-skimming-boom-US-Coast-Guard-May-31-2010.jpg)](https:\/\/cdn.britannica.com\/28\/142528-004-3BC77414\/oil-coast-skimming-boom-US-Coast-Guard-May-31-2010.jpg)   [![Deepwater Horizon oil spill: Pensacola Beach](https:\/\/cdn.britannica.com\/31\/142531-004-A176E25D\/Sand-oil-spill-Deepwater-Horizon-Fla-Pensacola-2010.jpg)](https:\/\/cdn.britannica.com\/31\/142531-050-7E758C72\/Sand-oil-spill-Deepwater-Horizon-Fla-Pensacola-2010.jpg)\n\nQuizzes\n\n[![Warm water fuels Hurricane Katrina. This image depicts a 3-day average of actual dea surface temperatures for the Caribbean Sea and Atlantic Ocean, from August 25-27, 2005.](https:\/\/cdn.britannica.com\/49\/93649-131-FB06761E\/Satellite-image-sea-surface-temperatures-display-Hurricane-Aug-27-2005.jpg?w=200&h=200&c=crop)](https:\/\/www.britannica.com\/quiz\/disasters-of-historic-proportion)\n\n[Disasters of Historic Proportion](https:\/\/www.britannica.com\/quiz\/disasters-of-historic-proportion)\n\nRelated Questions\n\n- [What caused the Deepwater Horizon oil spill?](https:\/\/www.britannica.com\/question\/What-caused-the-Deepwater-Horizon-oil-spill)\n- [How did the Deepwater Horizon oil spill affect birds?](https:\/\/www.britannica.com\/question\/How-did-the-Deepwater-Horizon-oil-spill-affect-birds)\n- [What caused the Camp Fire in 2018?](https:\/\/www.britannica.com\/question\/What-caused-the-Camp-Fire-in-2018)\n- [What caused the *Eastland* disaster?](https:\/\/www.britannica.com\/question\/What-caused-the-Eastland-disaster)\n- [What happened to the SS *Eastland*?](https:\/\/www.britannica.com\/question\/What-happened-to-the-SS-Eastland)\n\n![Britannica AI Icon](https:\/\/cdn.britannica.com\/mendel-resources\/3-179\/images\/chatbot\/star-ai.svg?v=3.179.9)\n\n[World History](https:\/\/www.britannica.com\/browse\/World-History)    [Accidents & Disasters](https:\/\/www.britannica.com\/browse\/Accidents-Disasters)\n\n*print* Print\n\nPlease select which sections you would like to print:\n\nCITE\n\n*verified*Cite\n\nWhile every effort has been made to follow citation style rules, there may be some discrepancies. Please refer to the appropriate style manual or other sources if you have any questions.\n\nSelect Citation Style\n\nCopy Citation\n\nShare\n\nShare\n\nShare to social media\n\n[Facebook](https:\/\/www.facebook.com\/BRITANNICA\/) [X](https:\/\/x.com\/britannica)\n\nURL\n\n<https:\/\/www.britannica.com\/event\/Deepwater-Horizon-oil-spill>\n\nFeedback\n\nExternal Websites\n\nFeedback\n\nThank you for your feedback\n\nOur editors will review what you’ve submitted and determine whether to revise the article.\n\nExternal Websites\n\n- [Smithsonian Ocean - Gulf Oil Spill](https:\/\/ocean.si.edu\/conservation\/pollution\/gulf-oil-spill)\n- [National Ocean Service - Deepwater Horizon Oil Spill](https:\/\/oceanservice.noaa.gov\/news\/apr17\/dwh-protected-species.html)\n- [Frontiers \\| Fates of petroleum during the deepwater horizon oil spill: A chemistry perspective](https:\/\/www.frontiersin.org\/journals\/marine-science\/articles\/10.3389\/fmars.2022.928576\/full)\n- [Center for Biological Diversity - A Deadly Toll](https:\/\/www.biologicaldiversity.org\/programs\/public_lands\/energy\/dirty_energy_development\/oil_and_gas\/gulf_oil_spill\/a_deadly_toll.html)\n- [National Center for Biotechnology Information - PubMed Central - Improving the Integration of Restoration and Conservation in Marine and Coastal Ecosystems: Lessons from the Deepwater Horizon Disaster](https:\/\/pmc.ncbi.nlm.nih.gov\/articles\/PMC6829012\/)\n- [Texas Parks and Wildlife - Deepwater Horizon Oil Spill](https:\/\/tpwd.texas.gov\/landwater\/water\/environconcerns\/damage_assessment\/dwh_spill\/)\n- [Marine Mammal Commission - Deepwater Horizon Oil Spill in the Gulf of Mexico](https:\/\/www.mmc.gov\/priority-topics\/offshore-energy-development-and-marine-mammals\/gulf-of-mexico-deepwater-horizon-oil-spill-and-marine-mammals\/)\n- [BBC - The Documentary Podcast - Deepwater Horizon oil spill](https:\/\/www.bbc.com\/audio\/play\/p09lx4jf)\n- [The Oceanography Society - Human Health and Socioeconomic Effects of the Deepwater Horizon Oil Spill in the Gulf of Mexico](https:\/\/tos.org\/oceanography\/article\/human-health-and-socioeconomic-effects-of-the-deepwater-horizon-oil-spill-in-the-gulf-of-mexico-1)\n- [PNAS - Science in support of the Deepwater Horizon response](https:\/\/www.pnas.org\/doi\/10.1073\/pnas.1204729109)\n\nBritannica Websites\n\nArticles from Britannica Encyclopedias for elementary and high school students.\n\n- [Deepwater Horizon oil spill of 2010 - Student Encyclopedia (Ages 11 and up)](https:\/\/kids.britannica.com\/students\/article\/Deepwater-Horizon-oil-spill-of-2010\/544332)\n\n[![Deepwater Horizon oil rig: fire](https:\/\/cdn.britannica.com\/58\/139558-050-9EEE9E93\/Fireboat-response-crews-blaze-oil-rig-Deepwater-April-21-2010.jpg?w=400&h=300&c=crop)](https:\/\/cdn.britannica.com\/58\/139558-050-9EEE9E93\/Fireboat-response-crews-blaze-oil-rig-Deepwater-April-21-2010.jpg)\n\n[Deepwater Horizon oil rig: fire](https:\/\/cdn.britannica.com\/58\/139558-050-9EEE9E93\/Fireboat-response-crews-blaze-oil-rig-Deepwater-April-21-2010.jpg) Fireboat response crews attempting to extinguish the blaze aboard the Deepwater Horizon oil rig in the Gulf of Mexico, April 21, 2010.\n\n(more)\n\n# Deepwater Horizon oil spill\nenvironmental disaster, Gulf of Mexico \\[2010\\]\n\nAsk Anything\n\nQuick Summary\n\nHomework Help\n\nWritten by\n\n[Richard Pallardy Richard Pallardy received a B.A. in English from Illinois State University in 2005. He was a research editor with Encyclopaedia Britannica, Inc. from 2008 to 2016 and worked on Britannica Blog from 2010...](https:\/\/www.britannica.com\/editor\/Richard-Pallardy\/6744)\n\nRichard Pallardy\n\nFact-checked by\n\n[Britannica Editors Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree....](https:\/\/www.britannica.com\/editor\/The-Editors-of-Encyclopaedia-Britannica\/4419)\n\nBritannica Editors\n\nLast updated\n\nApr. 13, 2026\n\n•[History](https:\/\/www.britannica.com\/event\/Deepwater-Horizon-oil-spill\/additional-info#history)\n\n![Britannica AI Icon](https:\/\/cdn.britannica.com\/mendel-resources\/3-179\/images\/chatbot\/star-ai.svg?v=3.179.9) Britannica AI\n\nAsk Anything\n\nQuick Summary\n\nTable of Contents\n\nTable of Contents\n\nQuick Summary\n\nAsk Anything\n\nTop Questions\n\n### When did the Deepwater Horizon oil spill happen?\nThe Deepwater Horizon oil spill began on April 20, 2010, when an explosion damaged the Deepwater Horizon oil rig. The rig’s sinking on April 22 began the discharge of oil into the Gulf of Mexico.\n\n### Who owned the rig responsible for the Deepwater Horizon oil spill?\nThe oil rig involved in the Deepwater Horizon oil spill was owned and operated by offshore oil-drilling company Transocean and leased by the oil company [BP](https:\/\/www.britannica.com\/money\/BP-PLC).\n\n### What caused the Deepwater Horizon oil spill?\nThe Deepwater Horizon oil spill occurred after a surge of natural gas blasted through a concrete core recently installed to seal an oil well for later use. Once released, the natural gas traveled up a riser to the platform of the Deepwater Horizon oil rig that was over the well, where it ignited, killing 11 workers and injuring 17.\n\n### How did the Deepwater Horizon oil spill affect birds?\nBirds were particularly vulnerable to the effects of the Deepwater Horizon oil spill. Many died from ingesting oil or because it interfered with their ability to regulate their body temperatures. Brown pelicans and laughing gulls were among the species most affected. A study showed that up to 800,000 birds were thought to have died.\n\n[![Deepwater Horizon oil spill: debris and oil](https:\/\/cdn.britannica.com\/59\/139559-050-B9437E07\/Debris-oil-rig-Deepwater-Horizon-April-22-2010.jpg?w=300)](https:\/\/cdn.britannica.com\/59\/139559-050-B9437E07\/Debris-oil-rig-Deepwater-Horizon-April-22-2010.jpg)\n\n[Deepwater Horizon oil spill: debris and oil](https:\/\/cdn.britannica.com\/59\/139559-050-B9437E07\/Debris-oil-rig-Deepwater-Horizon-April-22-2010.jpg)Debris and oil from the Deepwater Horizon oil rig after it sank on April 22, 2010.\n\n(more)\n\n**Deepwater Horizon oil spill**, largest marine [oil spill](https:\/\/www.britannica.com\/science\/oil-spill) in history, caused by an April 20, 2010, explosion on the [Deepwater Horizon](https:\/\/www.britannica.com\/topic\/Deepwater-Horizon) oil rig—located in the [Gulf of Mexico](https:\/\/www.britannica.com\/place\/Gulf-of-Mexico-Gulf-of-America), approximately 41 miles (66 km) off the coast of [Louisiana](https:\/\/www.britannica.com\/place\/Louisiana-state)—and its [subsequent](https:\/\/www.britannica.com\/dictionary\/subsequent) sinking on April 22.\n\n## The explosion\n[![Observe fireboat responding to crews battling the fire during the Deepwater Horizon oil spill of 2010](https:\/\/cdn.britannica.com\/35\/139435-138-1AC5B657\/Fireboat-response-crews-remnants-offshore-oil-rig-April-21-2010.jpg?w=800&h=450&c=crop)](https:\/\/www.britannica.com\/video\/Fireboat-response-crews-remnants-offshore-oil-rig-April-21-2010\/-142250)\n\nObserve fireboat responding to crews battling the fire during the Deepwater Horizon oil spill of 2010Fireboat response crews battling the blazing remnants of the offshore oil rig Deepwater Horizon in the Gulf of Mexico, April 21, 2010.\n\n(more)\n\n[See all videos for this article](https:\/\/www.britannica.com\/event\/Deepwater-Horizon-oil-spill\/images-videos)\n\nThe Deepwater Horizon rig, owned and operated by offshore-oil-drilling company Transocean and leased by [oil](https:\/\/www.britannica.com\/science\/petroleum) company [BP](https:\/\/www.britannica.com\/money\/BP-PLC), was situated in the Macondo oil prospect in the Mississippi Canyon, a valley in the [continental shelf](https:\/\/www.britannica.com\/science\/continental-shelf). The oil well over which it was positioned was located on the seabed 4,993 feet (1,522 metres) below the surface and extended approximately 18,000 feet (5,486 metres) into the [rock](https:\/\/www.britannica.com\/science\/rock-geology). On the night of April 20 a surge of [natural gas](https:\/\/www.britannica.com\/science\/natural-gas) blasted through a [concrete](https:\/\/www.britannica.com\/technology\/concrete-building-material) core recently installed by contractor [Halliburton](https:\/\/www.britannica.com\/money\/Halliburton) in order to seal the well for later use. It later emerged through documents released by [Wikileaks](https:\/\/www.britannica.com\/topic\/WikiLeaks) that a similar incident had occurred on a BP-owned [rig](https:\/\/www.britannica.com\/dictionary\/rig) in the [Caspian Sea](https:\/\/www.britannica.com\/place\/Caspian-Sea) in September 2008. Both cores were likely too weak to withstand the pressure because they were composed of a [concrete](https:\/\/www.britannica.com\/technology\/concrete-building-material) mixture that used [nitrogen](https:\/\/www.britannica.com\/science\/nitrogen) gas to accelerate curing.\n\nOnce released by the fracture of the core, the [natural gas](https:\/\/www.britannica.com\/science\/natural-gas) traveled up the Deepwater rig’s riser to the platform, where it ignited, killing 11 workers and injuring 17. The rig capsized and sank on the morning of April 22, rupturing the riser, through which [drilling mud](https:\/\/www.britannica.com\/technology\/drilling-mud) had been injected in order to counteract the upward [pressure](https:\/\/www.britannica.com\/science\/pressure) of oil and natural gas. Without any opposing [force](https:\/\/www.britannica.com\/science\/force-physics), oil began to [discharge](https:\/\/www.britannica.com\/dictionary\/discharge) into the gulf. The volume of oil escaping the damaged well—originally estimated by BP to be about 1,000 barrels per day—was thought by U.S. [government](https:\/\/www.britannica.com\/topic\/government) officials to have peaked at more than 60,000 barrels per day.\n\n## Leaking oil\n[![Deepwater Horizon oil spill of 2010: path of the oil](https:\/\/cdn.britannica.com\/13\/144913-050-B931EC84\/Map-oil-spill-effects-Deepwater-Horizon-explosion-April-20-2010.jpg)1 of 2](https:\/\/cdn.britannica.com\/13\/144913-050-B931EC84\/Map-oil-spill-effects-Deepwater-Horizon-explosion-April-20-2010.jpg)\n\n[Deepwater Horizon oil spill of 2010: path of the oil](https:\/\/cdn.britannica.com\/13\/144913-050-B931EC84\/Map-oil-spill-effects-Deepwater-Horizon-explosion-April-20-2010.jpg)Map depicting the effects of the Deepwater Horizon oil spill, caused by the explosion of an oil rig off the coast of Louisiana on April 20, 2010. Scientists noted that the prevailing paths of the Gulf of Mexico's Loop Current and a detached eddy located to the west kept much of the oil, which covered a sizable part of the gulf some three months after the accident, from reaching shore.\n\n(more)\n\n[![See how wire entanglement inside a well bore mitigates the effects of blowout preventer failure in an oil well](https:\/\/cdn.britannica.com\/77\/186377-138-E57058AA\/use-obstruction-wire-effects-oil-well-blowout.jpg?w=800&h=450&c=crop)2 of 2](https:\/\/www.britannica.com\/video\/use-obstruction-wire-effects-oil-well-blowout\/-204448)\n\nSee how wire entanglement inside a well bore mitigates the effects of blowout preventer failure in an oil wellLearn about the experimental use of entangled wire as an obstruction to mitigate the effects of blowout preventer failure in an oil well.\n\n(more)\n\n[See all videos for this article](https:\/\/www.britannica.com\/event\/Deepwater-Horizon-oil-spill\/images-videos)\n\nAlthough [BP](https:\/\/www.britannica.com\/money\/BP-PLC) attempted to activate the rig’s blowout preventer (BOP), a fail-safe mechanism designed to close the channel through which oil was drawn, the device malfunctioned. [Forensic](https:\/\/www.merriam-webster.com\/dictionary\/Forensic) analysis of the BOP completed the following year determined that a set of massive blades known as blind shear rams—designed to slice through the pipe carrying oil—had malfunctioned because the pipe had bent under the pressure of the rising gas and oil. (A 2014 report by the U.S. Chemical Safety Board claimed that the blind shear rams had activated sooner than previously thought and may have actually punctured the pipe.)\n\nEfforts in May to place a containment dome over the largest leak in the broken riser were thwarted by the buoyant action of gas [hydrates](https:\/\/www.britannica.com\/science\/hydrate)—gas molecules in an ice matrix—formed by the reaction of natural gas and cold water. When an attempt to employ a “top kill,” whereby [drilling mud](https:\/\/www.britannica.com\/technology\/drilling-mud) was pumped into the well to stanch the flow of oil, also failed, BP in early June turned to an apparatus called the Lower Marine Riser Package (LMRP) cap. With the damaged riser shorn from the LMRP—the top segment of the BOP—the cap was lowered into place. Though fitted loosely over the BOP and allowing some oil to escape, the cap enabled BP to [siphon](https:\/\/www.britannica.com\/technology\/siphon-instrument) approximately 15,000 barrels of oil per day to a [tanker](https:\/\/www.britannica.com\/technology\/tanker). The addition of an [ancillary](https:\/\/www.merriam-webster.com\/dictionary\/ancillary) collection system [comprising](https:\/\/www.merriam-webster.com\/dictionary\/comprising) several devices, also tapped into the BOP, increased the collection rate to approximately 25,000 barrels of oil a day.\n\n[![Warm water fuels Hurricane Katrina. This image depicts a 3-day average of actual dea surface temperatures for the Caribbean Sea and Atlantic Ocean, from August 25-27, 2005.](https:\/\/cdn.britannica.com\/49\/93649-131-FB06761E\/Satellite-image-sea-surface-temperatures-display-Hurricane-Aug-27-2005.jpg) Britannica Quiz Disasters of Historic Proportion](https:\/\/www.britannica.com\/quiz\/disasters-of-historic-proportion)\n\nIn early July the LMRP cap was removed for several days so that a more permanent seal could be installed; this capping stack was in place by July 12. Though the leak had slowed, it was estimated by a government-commissioned panel of scientists that 4,900,000 barrels of oil had already leaked into the gulf. Only about 800,000 barrels had been captured. On August 3 BP conducted a “static kill,” a procedure in which drilling mud was pumped into the well through the [BOP](https:\/\/www.britannica.com\/dictionary\/BOP). Though similar to the failed top kill, mud could be injected at much lower pressures during the static kill because of the stabilizing influence of the capping stack. The defective BOP and the capping stack were removed in early September and replaced by a functioning BOP.\n\nThe success of these procedures cleared the way for a “bottom kill,” considered to be the most likely means of permanently sealing the leak. This entailed pumping [cement](https:\/\/www.britannica.com\/technology\/cement-building-material) through a channel—known as a relief well—that paralleled and eventually intersected the original well. Construction of two such wells had begun in May. On September 17 the bottom kill maneuver was successfully executed through the first relief well. The second had been intended to serve as a [backup](https:\/\/www.britannica.com\/dictionary\/backup) and was not completed. Two days later, following a series of pressure tests, it was announced that the well was completely sealed.\n\nQuick Facts\n\nAlso called:\n\nGulf of Mexico oil spill\n\n*(Show more)*\n\nDate:\n\nApril 20, 2010 - September 19, 2010 *(Anniversary in 4 days)*\n\n*(Show more)*\n\nLocation:\n\n[Gulf Coast](https:\/\/www.britannica.com\/place\/Gulf-Coast)\n\n[Gulf of Mexico \/ Gulf of America](https:\/\/www.britannica.com\/place\/Gulf-of-Mexico-Gulf-of-America)\n\n*(Show more)*\n\nContext:\n\n[drilling mud](https:\/\/www.britannica.com\/technology\/drilling-mud)\n\n[offshore drilling](https:\/\/www.britannica.com\/technology\/offshore-drilling)\n\n*(Show more)*\n\nKey People:\n\n[Luther Strange](https:\/\/www.britannica.com\/biography\/Luther-Strange)\n\n*(Show more)*\n\n[See all related content](https:\/\/www.britannica.com\/facts\/Deepwater-Horizon-oil-spill)\n\nExplore Britannica Premium\\!\n\nTrusted knowledge for those who want to know more.\n\n[SUBSCRIBE](https:\/\/premium.britannica.com\/premium-membership\/?utm_source=premium&utm_medium=inline-cta&utm_campaign=shorter-2026)\n\n![Penguin, ship, mountain, atlas](https:\/\/cdn.britannica.com\/marketing\/inline-left.webp)\n\n![shohei ohtani, plants, andy wharhol art](https:\/\/cdn.britannica.com\/marketing\/inline-right.webp)\n\n![Mobile](https:\/\/cdn.britannica.com\/marketing\/inline-mobile.webp?w=400)\n\nClaims by several research groups that subsurface plumes of dispersed [hydrocarbons](https:\/\/www.britannica.com\/science\/hydrocarbon) had been detected in May were initially dismissed by BP and the [National Oceanic and Atmospheric Administration](https:\/\/www.britannica.com\/topic\/National-Oceanic-and-Atmospheric-Administration) (NOAA). However, it was verified in June that the plumes were in fact from the Deepwater spill. The effect of the microscopic oil droplets on the ecosystem was unknown, though their presence, along with that of a layer of oil several inches thick discovered on portions of the seafloor in September, cast doubt on earlier [predictions](https:\/\/www.britannica.com\/dictionary\/predictions) about the speed with which the discharged oil would dissipate. [Bacteria](https:\/\/www.britannica.com\/science\/bacteria) that had adapted to consuming naturally occurring gas and oil seeping from the seabed were thought to have consumed a portion of it.","attrs_readable_markdown":"Top Questions\n\n### When did the Deepwater Horizon oil spill happen?\n### Who owned the rig responsible for the Deepwater Horizon oil spill?\n### What caused the Deepwater Horizon oil spill?\n### How did the Deepwater Horizon oil spill affect birds?\n\n**Deepwater Horizon oil spill**, largest marine [oil spill](https:\/\/www.britannica.com\/science\/oil-spill) in history, caused by an April 20, 2010, explosion on the [Deepwater Horizon](https:\/\/www.britannica.com\/topic\/Deepwater-Horizon) oil rig—located in the [Gulf of Mexico](https:\/\/www.britannica.com\/place\/Gulf-of-Mexico-Gulf-of-America), approximately 41 miles (66 km) off the coast of [Louisiana](https:\/\/www.britannica.com\/place\/Louisiana-state)—and its [subsequent](https:\/\/www.britannica.com\/dictionary\/subsequent) sinking on April 22.\n\n## The explosion\nObserve fireboat responding to crews battling the fire during the Deepwater Horizon oil spill of 2010Fireboat response crews battling the blazing remnants of the offshore oil rig Deepwater Horizon in the Gulf of Mexico, April 21, 2010.\n\n[See all videos for this article](https:\/\/www.britannica.com\/event\/Deepwater-Horizon-oil-spill\/images-videos)\n\nThe Deepwater Horizon rig, owned and operated by offshore-oil-drilling company Transocean and leased by [oil](https:\/\/www.britannica.com\/science\/petroleum) company [BP](https:\/\/www.britannica.com\/money\/BP-PLC), was situated in the Macondo oil prospect in the Mississippi Canyon, a valley in the [continental shelf](https:\/\/www.britannica.com\/science\/continental-shelf). The oil well over which it was positioned was located on the seabed 4,993 feet (1,522 metres) below the surface and extended approximately 18,000 feet (5,486 metres) into the [rock](https:\/\/www.britannica.com\/science\/rock-geology). On the night of April 20 a surge of [natural gas](https:\/\/www.britannica.com\/science\/natural-gas) blasted through a [concrete](https:\/\/www.britannica.com\/technology\/concrete-building-material) core recently installed by contractor [Halliburton](https:\/\/www.britannica.com\/money\/Halliburton) in order to seal the well for later use. It later emerged through documents released by [Wikileaks](https:\/\/www.britannica.com\/topic\/WikiLeaks) that a similar incident had occurred on a BP-owned [rig](https:\/\/www.britannica.com\/dictionary\/rig) in the [Caspian Sea](https:\/\/www.britannica.com\/place\/Caspian-Sea) in September 2008. Both cores were likely too weak to withstand the pressure because they were composed of a [concrete](https:\/\/www.britannica.com\/technology\/concrete-building-material) mixture that used [nitrogen](https:\/\/www.britannica.com\/science\/nitrogen) gas to accelerate curing.\n\nOnce released by the fracture of the core, the [natural gas](https:\/\/www.britannica.com\/science\/natural-gas) traveled up the Deepwater rig’s riser to the platform, where it ignited, killing 11 workers and injuring 17. The rig capsized and sank on the morning of April 22, rupturing the riser, through which [drilling mud](https:\/\/www.britannica.com\/technology\/drilling-mud) had been injected in order to counteract the upward [pressure](https:\/\/www.britannica.com\/science\/pressure) of oil and natural gas. Without any opposing [force](https:\/\/www.britannica.com\/science\/force-physics), oil began to [discharge](https:\/\/www.britannica.com\/dictionary\/discharge) into the gulf. The volume of oil escaping the damaged well—originally estimated by BP to be about 1,000 barrels per day—was thought by U.S. [government](https:\/\/www.britannica.com\/topic\/government) officials to have peaked at more than 60,000 barrels per day.\n\n## Leaking oil\nAlthough [BP](https:\/\/www.britannica.com\/money\/BP-PLC) attempted to activate the rig’s blowout preventer (BOP), a fail-safe mechanism designed to close the channel through which oil was drawn, the device malfunctioned. [Forensic](https:\/\/www.merriam-webster.com\/dictionary\/Forensic) analysis of the BOP completed the following year determined that a set of massive blades known as blind shear rams—designed to slice through the pipe carrying oil—had malfunctioned because the pipe had bent under the pressure of the rising gas and oil. (A 2014 report by the U.S. Chemical Safety Board claimed that the blind shear rams had activated sooner than previously thought and may have actually punctured the pipe.)\n\nEfforts in May to place a containment dome over the largest leak in the broken riser were thwarted by the buoyant action of gas [hydrates](https:\/\/www.britannica.com\/science\/hydrate)—gas molecules in an ice matrix—formed by the reaction of natural gas and cold water. When an attempt to employ a “top kill,” whereby [drilling mud](https:\/\/www.britannica.com\/technology\/drilling-mud) was pumped into the well to stanch the flow of oil, also failed, BP in early June turned to an apparatus called the Lower Marine Riser Package (LMRP) cap. With the damaged riser shorn from the LMRP—the top segment of the BOP—the cap was lowered into place. Though fitted loosely over the BOP and allowing some oil to escape, the cap enabled BP to [siphon](https:\/\/www.britannica.com\/technology\/siphon-instrument) approximately 15,000 barrels of oil per day to a [tanker](https:\/\/www.britannica.com\/technology\/tanker). The addition of an [ancillary](https:\/\/www.merriam-webster.com\/dictionary\/ancillary) collection system [comprising](https:\/\/www.merriam-webster.com\/dictionary\/comprising) several devices, also tapped into the BOP, increased the collection rate to approximately 25,000 barrels of oil a day.\n\n[![Warm water fuels Hurricane Katrina. This image depicts a 3-day average of actual dea surface temperatures for the Caribbean Sea and Atlantic Ocean, from August 25-27, 2005.](https:\/\/cdn.britannica.com\/49\/93649-131-FB06761E\/Satellite-image-sea-surface-temperatures-display-Hurricane-Aug-27-2005.jpg) Britannica Quiz Disasters of Historic Proportion](https:\/\/www.britannica.com\/quiz\/disasters-of-historic-proportion)\n\nIn early July the LMRP cap was removed for several days so that a more permanent seal could be installed; this capping stack was in place by July 12. Though the leak had slowed, it was estimated by a government-commissioned panel of scientists that 4,900,000 barrels of oil had already leaked into the gulf. Only about 800,000 barrels had been captured. On August 3 BP conducted a “static kill,” a procedure in which drilling mud was pumped into the well through the [BOP](https:\/\/www.britannica.com\/dictionary\/BOP). Though similar to the failed top kill, mud could be injected at much lower pressures during the static kill because of the stabilizing influence of the capping stack. The defective BOP and the capping stack were removed in early September and replaced by a functioning BOP.\n\nThe success of these procedures cleared the way for a “bottom kill,” considered to be the most likely means of permanently sealing the leak. This entailed pumping [cement](https:\/\/www.britannica.com\/technology\/cement-building-material) through a channel—known as a relief well—that paralleled and eventually intersected the original well. Construction of two such wells had begun in May. On September 17 the bottom kill maneuver was successfully executed through the first relief well. The second had been intended to serve as a [backup](https:\/\/www.britannica.com\/dictionary\/backup) and was not completed. Two days later, following a series of pressure tests, it was announced that the well was completely sealed.\n\nQuick Facts\n\nAlso called:\n\nGulf of Mexico oil spill\n\nDate:\n\nApril 20, 2010 - September 19, 2010 *(Anniversary in 4 days)*\n\nTrusted knowledge for those who want to know more.\n\n[SUBSCRIBE](https:\/\/premium.britannica.com\/premium-membership\/?utm_source=premium&utm_medium=inline-cta&utm_campaign=shorter-2026)\n\n![Penguin, ship, mountain, atlas](https:\/\/cdn.britannica.com\/marketing\/inline-left.webp)\n\n![shohei ohtani, plants, andy wharhol art](https:\/\/cdn.britannica.com\/marketing\/inline-right.webp)\n\n![Mobile](https:\/\/cdn.britannica.com\/marketing\/inline-mobile.webp?w=400)\n\nClaims by several research groups that subsurface plumes of dispersed [hydrocarbons](https:\/\/www.britannica.com\/science\/hydrocarbon) had been detected in May were initially dismissed by BP and the [National Oceanic and Atmospheric Administration](https:\/\/www.britannica.com\/topic\/National-Oceanic-and-Atmospheric-Administration) (NOAA). However, it was verified in June that the plumes were in fact from the Deepwater spill. The effect of the microscopic oil droplets on the ecosystem was unknown, though their presence, along with that of a layer of oil several inches thick discovered on portions of the seafloor in September, cast doubt on earlier [predictions](https:\/\/www.britannica.com\/dictionary\/predictions) about the speed with which the discharged oil would dissipate. [Bacteria](https:\/\/www.britannica.com\/science\/bacteria) that had adapted to consuming naturally occurring gas and oil seeping from the seabed were thought to have consumed a portion of it.","meta_canonical":null}

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Meta Description	Deepwater Horizon oil spill, largest marine oil spill in history, caused by an April 20, 2010, explosion on the Deepwater Horizon oil rig—located in the Gulf of Mexico, approximately 41 miles (66 km) off the coast of Louisiana—and its subsequent sinking on April 22.
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Boilerpipe Text	Top Questions When did the Deepwater Horizon oil spill happen? Who owned the rig responsible for the Deepwater Horizon oil spill? What caused the Deepwater Horizon oil spill? How did the Deepwater Horizon oil spill affect birds? Deepwater Horizon oil spill , largest marine oil spill in history, caused by an April 20, 2010, explosion on the Deepwater Horizon oil rig—located in the Gulf of Mexico , approximately 41 miles (66 km) off the coast of Louisiana —and its subsequent sinking on April 22. The explosion Observe fireboat responding to crews battling the fire during the Deepwater Horizon oil spill of 2010 Fireboat response crews battling the blazing remnants of the offshore oil rig Deepwater Horizon in the Gulf of Mexico, April 21, 2010. See all videos for this article The Deepwater Horizon rig, owned and operated by offshore-oil-drilling company Transocean and leased by oil company BP , was situated in the Macondo oil prospect in the Mississippi Canyon, a valley in the continental shelf . The oil well over which it was positioned was located on the seabed 4,993 feet (1,522 metres) below the surface and extended approximately 18,000 feet (5,486 metres) into the rock . On the night of April 20 a surge of natural gas blasted through a concrete core recently installed by contractor Halliburton in order to seal the well for later use. It later emerged through documents released by Wikileaks that a similar incident had occurred on a BP-owned rig in the Caspian Sea in September 2008. Both cores were likely too weak to withstand the pressure because they were composed of a concrete mixture that used nitrogen gas to accelerate curing. Once released by the fracture of the core, the natural gas traveled up the Deepwater rig’s riser to the platform, where it ignited, killing 11 workers and injuring 17. The rig capsized and sank on the morning of April 22, rupturing the riser, through which drilling mud had been injected in order to counteract the upward pressure of oil and natural gas. Without any opposing force , oil began to discharge into the gulf. The volume of oil escaping the damaged well—originally estimated by BP to be about 1,000 barrels per day—was thought by U.S. government officials to have peaked at more than 60,000 barrels per day. Leaking oil Although BP attempted to activate the rig’s blowout preventer (BOP), a fail-safe mechanism designed to close the channel through which oil was drawn, the device malfunctioned. Forensic analysis of the BOP completed the following year determined that a set of massive blades known as blind shear rams—designed to slice through the pipe carrying oil—had malfunctioned because the pipe had bent under the pressure of the rising gas and oil. (A 2014 report by the U.S. Chemical Safety Board claimed that the blind shear rams had activated sooner than previously thought and may have actually punctured the pipe.) Efforts in May to place a containment dome over the largest leak in the broken riser were thwarted by the buoyant action of gas hydrates —gas molecules in an ice matrix—formed by the reaction of natural gas and cold water. When an attempt to employ a “ top kill,” whereby drilling mud was pumped into the well to stanch the flow of oil, also failed, BP in early June turned to an apparatus called the Lower Marine Riser Package (LMRP) cap. With the damaged riser shorn from the LMRP—the top segment of the BOP—the cap was lowered into place. Though fitted loosely over the BOP and allowing some oil to escape, the cap enabled BP to siphon approximately 15,000 barrels of oil per day to a tanker . The addition of an ancillary collection system comprising several devices, also tapped into the BOP, increased the collection rate to approximately 25,000 barrels of oil a day. Britannica Quiz Disasters of Historic Proportion In early July the LMRP cap was removed for several days so that a more permanent seal could be installed; this capping stack was in place by July 12. Though the leak had slowed, it was estimated by a government-commissioned panel of scientists that 4,900,000 barrels of oil had already leaked into the gulf. Only about 800,000 barrels had been captured. On August 3 BP conducted a “ static kill,” a procedure in which drilling mud was pumped into the well through the BOP . Though similar to the failed top kill, mud could be injected at much lower pressures during the static kill because of the stabilizing influence of the capping stack. The defective BOP and the capping stack were removed in early September and replaced by a functioning BOP. The success of these procedures cleared the way for a “ bottom kill,” considered to be the most likely means of permanently sealing the leak. This entailed pumping cement through a channel—known as a relief well—that paralleled and eventually intersected the original well. Construction of two such wells had begun in May. On September 17 the bottom kill maneuver was successfully executed through the first relief well. The second had been intended to serve as a backup and was not completed. Two days later, following a series of pressure tests, it was announced that the well was completely sealed. Quick Facts Also called: Gulf of Mexico oil spill Date: April 20, 2010 - September 19, 2010 (Anniversary in 4 days) Trusted knowledge for those who want to know more. SUBSCRIBE Claims by several research groups that subsurface plumes of dispersed hydrocarbons had been detected in May were initially dismissed by BP and the National Oceanic and Atmospheric Administration (NOAA). However, it was verified in June that the plumes were in fact from the Deepwater spill. The effect of the microscopic oil droplets on the ecosystem was unknown, though their presence, along with that of a layer of oil several inches thick discovered on portions of the seafloor in September, cast doubt on earlier predictions about the speed with which the discharged oil would dissipate. Bacteria that had adapted to consuming naturally occurring gas and oil seeping from the seabed were thought to have consumed a portion of it.
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[The Deepwater Horizon oil spill in pictures](https://www.britannica.com/event/Deepwater-Horizon-oil-spill/Environmental-costs#ref294128) [References & Edit History](https://www.britannica.com/event/Deepwater-Horizon-oil-spill/additional-info) [Quick Facts & Related Topics](https://www.britannica.com/facts/Deepwater-Horizon-oil-spill) [Images & Videos](https://www.britannica.com/event/Deepwater-Horizon-oil-spill/images-videos) [![Deepwater Horizon oil rig: fire](https://cdn.britannica.com/58/139558-004-2F1526EA/Fireboat-response-crews-blaze-oil-rig-Deepwater-April-21-2010.jpg)](https://cdn.britannica.com/58/139558-050-9EEE9E93/Fireboat-response-crews-blaze-oil-rig-Deepwater-April-21-2010.jpg) [![Deepwater Horizon oil spill: debris and oil](https://cdn.britannica.com/59/139559-004-71A72F92/Debris-oil-rig-Deepwater-Horizon-April-22-2010.jpg)](https://cdn.britannica.com/59/139559-050-B9437E07/Debris-oil-rig-Deepwater-Horizon-April-22-2010.jpg) [![Observe fireboat responding to crews battling the fire during the Deepwater Horizon oil spill of 2010](https://cdn.britannica.com/35/139435-138-1AC5B657/Fireboat-response-crews-remnants-offshore-oil-rig-April-21-2010.jpg?w=400&h=225&c=crop)](https://www.britannica.com/video/Fireboat-response-crews-remnants-offshore-oil-rig-April-21-2010/-142250) [![Deepwater Horizon oil spill of 2010: path of the oil](https://cdn.britannica.com/13/144913-004-DF74E60F/Map-oil-spill-effects-Deepwater-Horizon-explosion-April-20-2010.jpg)](https://cdn.britannica.com/13/144913-050-B931EC84/Map-oil-spill-effects-Deepwater-Horizon-explosion-April-20-2010.jpg) [![See how wire entanglement inside a well bore mitigates the effects of blowout preventer failure in an oil well](https://cdn.britannica.com/77/186377-138-E57058AA/use-obstruction-wire-effects-oil-well-blowout.jpg?w=400&h=225&c=crop)](https://www.britannica.com/video/use-obstruction-wire-effects-oil-well-blowout/-204448) [![Deepwater Horizon oil spill: controlled burn](https://cdn.britannica.com/49/141349-004-B78DD4D8/oil-burn-disaster-Deepwater-Horizon-Gulf-of-May-6-2010.jpg)](https://cdn.britannica.com/49/141349-050-4E645470/oil-burn-disaster-Deepwater-Horizon-Gulf-of-May-6-2010.jpg) [![Deepwater Horizon oil spill: beach cleanup](https://cdn.britannica.com/32/142532-004-915959E6/Workers-beach-oil-BP-Port-Fourchon-Louisiana-May-23-2010.jpg)](https://cdn.britannica.com/32/142532-050-827D3EE3/Workers-beach-oil-BP-Port-Fourchon-Louisiana-May-23-2010.jpg) [![Deepwater Horizon oil spill: avian casualty](https://cdn.britannica.com/52/141352-004-39C60C27/bird-oil-spill-Gulf-of-Mexico-Deepwater-June-2010.jpg)](https://cdn.britannica.com/52/141352-050-41B2F42A/bird-oil-spill-Gulf-of-Mexico-Deepwater-June-2010.jpg) [![Deepwater Horizon oil spill: skimming](https://cdn.britannica.com/28/142528-004-3BC77414/oil-coast-skimming-boom-US-Coast-Guard-May-31-2010.jpg)](https://cdn.britannica.com/28/142528-004-3BC77414/oil-coast-skimming-boom-US-Coast-Guard-May-31-2010.jpg) [![Deepwater Horizon oil spill: Pensacola Beach](https://cdn.britannica.com/31/142531-004-A176E25D/Sand-oil-spill-Deepwater-Horizon-Fla-Pensacola-2010.jpg)](https://cdn.britannica.com/31/142531-050-7E758C72/Sand-oil-spill-Deepwater-Horizon-Fla-Pensacola-2010.jpg) Quizzes [![Warm water fuels Hurricane Katrina. This image depicts a 3-day average of actual dea surface temperatures for the Caribbean Sea and Atlantic Ocean, from August 25-27, 2005.](https://cdn.britannica.com/49/93649-131-FB06761E/Satellite-image-sea-surface-temperatures-display-Hurricane-Aug-27-2005.jpg?w=200&h=200&c=crop)](https://www.britannica.com/quiz/disasters-of-historic-proportion) [Disasters of Historic Proportion](https://www.britannica.com/quiz/disasters-of-historic-proportion) Related Questions - [What caused the Deepwater Horizon oil spill?](https://www.britannica.com/question/What-caused-the-Deepwater-Horizon-oil-spill) - [How did the Deepwater Horizon oil spill affect birds?](https://www.britannica.com/question/How-did-the-Deepwater-Horizon-oil-spill-affect-birds) - [What caused the Camp Fire in 2018?](https://www.britannica.com/question/What-caused-the-Camp-Fire-in-2018) - [What caused the Eastland disaster?](https://www.britannica.com/question/What-caused-the-Eastland-disaster) - [What happened to the SS Eastland?](https://www.britannica.com/question/What-happened-to-the-SS-Eastland) ![Britannica AI Icon](https://cdn.britannica.com/mendel-resources/3-179/images/chatbot/star-ai.svg?v=3.179.9) [World History](https://www.britannica.com/browse/World-History) [Accidents & Disasters](https://www.britannica.com/browse/Accidents-Disasters) print Print Please select which sections you would like to print: CITE verifiedCite While every effort has been made to follow citation style rules, there may be some discrepancies. 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External Websites - [Smithsonian Ocean - Gulf Oil Spill](https://ocean.si.edu/conservation/pollution/gulf-oil-spill) - [National Ocean Service - Deepwater Horizon Oil Spill](https://oceanservice.noaa.gov/news/apr17/dwh-protected-species.html) - [Frontiers \\| Fates of petroleum during the deepwater horizon oil spill: A chemistry perspective](https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2022.928576/full) - [Center for Biological Diversity - A Deadly Toll](https://www.biologicaldiversity.org/programs/public_lands/energy/dirty_energy_development/oil_and_gas/gulf_oil_spill/a_deadly_toll.html) - [National Center for Biotechnology Information - PubMed Central - Improving the Integration of Restoration and Conservation in Marine and Coastal Ecosystems: Lessons from the Deepwater Horizon Disaster](https://pmc.ncbi.nlm.nih.gov/articles/PMC6829012/) - [Texas Parks and Wildlife - Deepwater Horizon Oil Spill](https://tpwd.texas.gov/landwater/water/environconcerns/damage_assessment/dwh_spill/) - [Marine Mammal Commission - Deepwater Horizon Oil Spill in the Gulf of Mexico](https://www.mmc.gov/priority-topics/offshore-energy-development-and-marine-mammals/gulf-of-mexico-deepwater-horizon-oil-spill-and-marine-mammals/) - [BBC - The Documentary Podcast - Deepwater Horizon oil spill](https://www.bbc.com/audio/play/p09lx4jf) - [The Oceanography Society - Human Health and Socioeconomic Effects of the Deepwater Horizon Oil Spill in the Gulf of Mexico](https://tos.org/oceanography/article/human-health-and-socioeconomic-effects-of-the-deepwater-horizon-oil-spill-in-the-gulf-of-mexico-1) - [PNAS - Science in support of the Deepwater Horizon response](https://www.pnas.org/doi/10.1073/pnas.1204729109) Britannica Websites Articles from Britannica Encyclopedias for elementary and high school students. - [Deepwater Horizon oil spill of 2010 - Student Encyclopedia (Ages 11 and up)](https://kids.britannica.com/students/article/Deepwater-Horizon-oil-spill-of-2010/544332) [![Deepwater Horizon oil rig: fire](https://cdn.britannica.com/58/139558-050-9EEE9E93/Fireboat-response-crews-blaze-oil-rig-Deepwater-April-21-2010.jpg?w=400&h=300&c=crop)](https://cdn.britannica.com/58/139558-050-9EEE9E93/Fireboat-response-crews-blaze-oil-rig-Deepwater-April-21-2010.jpg) [Deepwater Horizon oil rig: fire](https://cdn.britannica.com/58/139558-050-9EEE9E93/Fireboat-response-crews-blaze-oil-rig-Deepwater-April-21-2010.jpg) Fireboat response crews attempting to extinguish the blaze aboard the Deepwater Horizon oil rig in the Gulf of Mexico, April 21, 2010. (more) # Deepwater Horizon oil spill environmental disaster, Gulf of Mexico \[2010\] Ask Anything Quick Summary Homework Help Written by [Richard Pallardy Richard Pallardy received a B.A. in English from Illinois State University in 2005. He was a research editor with Encyclopaedia Britannica, Inc. from 2008 to 2016 and worked on Britannica Blog from 2010...](https://www.britannica.com/editor/Richard-Pallardy/6744) Richard Pallardy Fact-checked by [Britannica Editors Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree....](https://www.britannica.com/editor/The-Editors-of-Encyclopaedia-Britannica/4419) Britannica Editors Last updated Apr. 13, 2026 •[History](https://www.britannica.com/event/Deepwater-Horizon-oil-spill/additional-info#history) ![Britannica AI Icon](https://cdn.britannica.com/mendel-resources/3-179/images/chatbot/star-ai.svg?v=3.179.9) Britannica AI Ask Anything Quick Summary Table of Contents Table of Contents Quick Summary Ask Anything Top Questions ### When did the Deepwater Horizon oil spill happen? The Deepwater Horizon oil spill began on April 20, 2010, when an explosion damaged the Deepwater Horizon oil rig. The rig’s sinking on April 22 began the discharge of oil into the Gulf of Mexico. ### Who owned the rig responsible for the Deepwater Horizon oil spill? The oil rig involved in the Deepwater Horizon oil spill was owned and operated by offshore oil-drilling company Transocean and leased by the oil company [BP](https://www.britannica.com/money/BP-PLC). ### What caused the Deepwater Horizon oil spill? The Deepwater Horizon oil spill occurred after a surge of natural gas blasted through a concrete core recently installed to seal an oil well for later use. Once released, the natural gas traveled up a riser to the platform of the Deepwater Horizon oil rig that was over the well, where it ignited, killing 11 workers and injuring 17. ### How did the Deepwater Horizon oil spill affect birds? Birds were particularly vulnerable to the effects of the Deepwater Horizon oil spill. Many died from ingesting oil or because it interfered with their ability to regulate their body temperatures. Brown pelicans and laughing gulls were among the species most affected. A study showed that up to 800,000 birds were thought to have died. [![Deepwater Horizon oil spill: debris and oil](https://cdn.britannica.com/59/139559-050-B9437E07/Debris-oil-rig-Deepwater-Horizon-April-22-2010.jpg?w=300)](https://cdn.britannica.com/59/139559-050-B9437E07/Debris-oil-rig-Deepwater-Horizon-April-22-2010.jpg) [Deepwater Horizon oil spill: debris and oil](https://cdn.britannica.com/59/139559-050-B9437E07/Debris-oil-rig-Deepwater-Horizon-April-22-2010.jpg)Debris and oil from the Deepwater Horizon oil rig after it sank on April 22, 2010. (more) Deepwater Horizon oil spill, largest marine [oil spill](https://www.britannica.com/science/oil-spill) in history, caused by an April 20, 2010, explosion on the [Deepwater Horizon](https://www.britannica.com/topic/Deepwater-Horizon) oil rig—located in the [Gulf of Mexico](https://www.britannica.com/place/Gulf-of-Mexico-Gulf-of-America), approximately 41 miles (66 km) off the coast of [Louisiana](https://www.britannica.com/place/Louisiana-state)—and its [subsequent](https://www.britannica.com/dictionary/subsequent) sinking on April 22. ## The explosion [![Observe fireboat responding to crews battling the fire during the Deepwater Horizon oil spill of 2010](https://cdn.britannica.com/35/139435-138-1AC5B657/Fireboat-response-crews-remnants-offshore-oil-rig-April-21-2010.jpg?w=800&h=450&c=crop)](https://www.britannica.com/video/Fireboat-response-crews-remnants-offshore-oil-rig-April-21-2010/-142250) Observe fireboat responding to crews battling the fire during the Deepwater Horizon oil spill of 2010Fireboat response crews battling the blazing remnants of the offshore oil rig Deepwater Horizon in the Gulf of Mexico, April 21, 2010. (more) [See all videos for this article](https://www.britannica.com/event/Deepwater-Horizon-oil-spill/images-videos) The Deepwater Horizon rig, owned and operated by offshore-oil-drilling company Transocean and leased by [oil](https://www.britannica.com/science/petroleum) company [BP](https://www.britannica.com/money/BP-PLC), was situated in the Macondo oil prospect in the Mississippi Canyon, a valley in the [continental shelf](https://www.britannica.com/science/continental-shelf). The oil well over which it was positioned was located on the seabed 4,993 feet (1,522 metres) below the surface and extended approximately 18,000 feet (5,486 metres) into the [rock](https://www.britannica.com/science/rock-geology). On the night of April 20 a surge of [natural gas](https://www.britannica.com/science/natural-gas) blasted through a [concrete](https://www.britannica.com/technology/concrete-building-material) core recently installed by contractor [Halliburton](https://www.britannica.com/money/Halliburton) in order to seal the well for later use. It later emerged through documents released by [Wikileaks](https://www.britannica.com/topic/WikiLeaks) that a similar incident had occurred on a BP-owned [rig](https://www.britannica.com/dictionary/rig) in the [Caspian Sea](https://www.britannica.com/place/Caspian-Sea) in September 2008. Both cores were likely too weak to withstand the pressure because they were composed of a [concrete](https://www.britannica.com/technology/concrete-building-material) mixture that used [nitrogen](https://www.britannica.com/science/nitrogen) gas to accelerate curing. Once released by the fracture of the core, the [natural gas](https://www.britannica.com/science/natural-gas) traveled up the Deepwater rig’s riser to the platform, where it ignited, killing 11 workers and injuring 17. The rig capsized and sank on the morning of April 22, rupturing the riser, through which [drilling mud](https://www.britannica.com/technology/drilling-mud) had been injected in order to counteract the upward [pressure](https://www.britannica.com/science/pressure) of oil and natural gas. Without any opposing [force](https://www.britannica.com/science/force-physics), oil began to [discharge](https://www.britannica.com/dictionary/discharge) into the gulf. The volume of oil escaping the damaged well—originally estimated by BP to be about 1,000 barrels per day—was thought by U.S. [government](https://www.britannica.com/topic/government) officials to have peaked at more than 60,000 barrels per day. ## Leaking oil [![Deepwater Horizon oil spill of 2010: path of the oil](https://cdn.britannica.com/13/144913-050-B931EC84/Map-oil-spill-effects-Deepwater-Horizon-explosion-April-20-2010.jpg)1 of 2](https://cdn.britannica.com/13/144913-050-B931EC84/Map-oil-spill-effects-Deepwater-Horizon-explosion-April-20-2010.jpg) [Deepwater Horizon oil spill of 2010: path of the oil](https://cdn.britannica.com/13/144913-050-B931EC84/Map-oil-spill-effects-Deepwater-Horizon-explosion-April-20-2010.jpg)Map depicting the effects of the Deepwater Horizon oil spill, caused by the explosion of an oil rig off the coast of Louisiana on April 20, 2010. Scientists noted that the prevailing paths of the Gulf of Mexico's Loop Current and a detached eddy located to the west kept much of the oil, which covered a sizable part of the gulf some three months after the accident, from reaching shore. (more) [![See how wire entanglement inside a well bore mitigates the effects of blowout preventer failure in an oil well](https://cdn.britannica.com/77/186377-138-E57058AA/use-obstruction-wire-effects-oil-well-blowout.jpg?w=800&h=450&c=crop)2 of 2](https://www.britannica.com/video/use-obstruction-wire-effects-oil-well-blowout/-204448) See how wire entanglement inside a well bore mitigates the effects of blowout preventer failure in an oil wellLearn about the experimental use of entangled wire as an obstruction to mitigate the effects of blowout preventer failure in an oil well. (more) [See all videos for this article](https://www.britannica.com/event/Deepwater-Horizon-oil-spill/images-videos) Although [BP](https://www.britannica.com/money/BP-PLC) attempted to activate the rig’s blowout preventer (BOP), a fail-safe mechanism designed to close the channel through which oil was drawn, the device malfunctioned. [Forensic](https://www.merriam-webster.com/dictionary/Forensic) analysis of the BOP completed the following year determined that a set of massive blades known as blind shear rams—designed to slice through the pipe carrying oil—had malfunctioned because the pipe had bent under the pressure of the rising gas and oil. (A 2014 report by the U.S. Chemical Safety Board claimed that the blind shear rams had activated sooner than previously thought and may have actually punctured the pipe.) Efforts in May to place a containment dome over the largest leak in the broken riser were thwarted by the buoyant action of gas [hydrates](https://www.britannica.com/science/hydrate)—gas molecules in an ice matrix—formed by the reaction of natural gas and cold water. When an attempt to employ a “top kill,” whereby [drilling mud](https://www.britannica.com/technology/drilling-mud) was pumped into the well to stanch the flow of oil, also failed, BP in early June turned to an apparatus called the Lower Marine Riser Package (LMRP) cap. With the damaged riser shorn from the LMRP—the top segment of the BOP—the cap was lowered into place. Though fitted loosely over the BOP and allowing some oil to escape, the cap enabled BP to [siphon](https://www.britannica.com/technology/siphon-instrument) approximately 15,000 barrels of oil per day to a [tanker](https://www.britannica.com/technology/tanker). The addition of an [ancillary](https://www.merriam-webster.com/dictionary/ancillary) collection system [comprising](https://www.merriam-webster.com/dictionary/comprising) several devices, also tapped into the BOP, increased the collection rate to approximately 25,000 barrels of oil a day. [![Warm water fuels Hurricane Katrina. This image depicts a 3-day average of actual dea surface temperatures for the Caribbean Sea and Atlantic Ocean, from August 25-27, 2005.](https://cdn.britannica.com/49/93649-131-FB06761E/Satellite-image-sea-surface-temperatures-display-Hurricane-Aug-27-2005.jpg) Britannica Quiz Disasters of Historic Proportion](https://www.britannica.com/quiz/disasters-of-historic-proportion) In early July the LMRP cap was removed for several days so that a more permanent seal could be installed; this capping stack was in place by July 12. Though the leak had slowed, it was estimated by a government-commissioned panel of scientists that 4,900,000 barrels of oil had already leaked into the gulf. Only about 800,000 barrels had been captured. On August 3 BP conducted a “static kill,” a procedure in which drilling mud was pumped into the well through the [BOP](https://www.britannica.com/dictionary/BOP). Though similar to the failed top kill, mud could be injected at much lower pressures during the static kill because of the stabilizing influence of the capping stack. The defective BOP and the capping stack were removed in early September and replaced by a functioning BOP. The success of these procedures cleared the way for a “bottom kill,” considered to be the most likely means of permanently sealing the leak. This entailed pumping [cement](https://www.britannica.com/technology/cement-building-material) through a channel—known as a relief well—that paralleled and eventually intersected the original well. Construction of two such wells had begun in May. On September 17 the bottom kill maneuver was successfully executed through the first relief well. The second had been intended to serve as a [backup](https://www.britannica.com/dictionary/backup) and was not completed. Two days later, following a series of pressure tests, it was announced that the well was completely sealed. Quick Facts Also called: Gulf of Mexico oil spill (Show more) Date: April 20, 2010 - September 19, 2010 (Anniversary in 4 days) (Show more) Location: [Gulf Coast](https://www.britannica.com/place/Gulf-Coast) [Gulf of Mexico / Gulf of America](https://www.britannica.com/place/Gulf-of-Mexico-Gulf-of-America) (Show more) Context: [drilling mud](https://www.britannica.com/technology/drilling-mud) [offshore drilling](https://www.britannica.com/technology/offshore-drilling) (Show more) Key People: [Luther Strange](https://www.britannica.com/biography/Luther-Strange) (Show more) [See all related content](https://www.britannica.com/facts/Deepwater-Horizon-oil-spill) Explore Britannica Premium\! Trusted knowledge for those who want to know more. [SUBSCRIBE](https://premium.britannica.com/premium-membership/?utm_source=premium&utm_medium=inline-cta&utm_campaign=shorter-2026) ![Penguin, ship, mountain, atlas](https://cdn.britannica.com/marketing/inline-left.webp) ![shohei ohtani, plants, andy wharhol art](https://cdn.britannica.com/marketing/inline-right.webp) ![Mobile](https://cdn.britannica.com/marketing/inline-mobile.webp?w=400) Claims by several research groups that subsurface plumes of dispersed [hydrocarbons](https://www.britannica.com/science/hydrocarbon) had been detected in May were initially dismissed by BP and the [National Oceanic and Atmospheric Administration](https://www.britannica.com/topic/National-Oceanic-and-Atmospheric-Administration) (NOAA). However, it was verified in June that the plumes were in fact from the Deepwater spill. The effect of the microscopic oil droplets on the ecosystem was unknown, though their presence, along with that of a layer of oil several inches thick discovered on portions of the seafloor in September, cast doubt on earlier [predictions](https://www.britannica.com/dictionary/predictions) about the speed with which the discharged oil would dissipate. [Bacteria](https://www.britannica.com/science/bacteria) that had adapted to consuming naturally occurring gas and oil seeping from the seabed were thought to have consumed a portion of it.
Readable Markdown	Top Questions ### When did the Deepwater Horizon oil spill happen? ### Who owned the rig responsible for the Deepwater Horizon oil spill? ### What caused the Deepwater Horizon oil spill? ### How did the Deepwater Horizon oil spill affect birds? Deepwater Horizon oil spill, largest marine [oil spill](https://www.britannica.com/science/oil-spill) in history, caused by an April 20, 2010, explosion on the [Deepwater Horizon](https://www.britannica.com/topic/Deepwater-Horizon) oil rig—located in the [Gulf of Mexico](https://www.britannica.com/place/Gulf-of-Mexico-Gulf-of-America), approximately 41 miles (66 km) off the coast of [Louisiana](https://www.britannica.com/place/Louisiana-state)—and its [subsequent](https://www.britannica.com/dictionary/subsequent) sinking on April 22. ## The explosion Observe fireboat responding to crews battling the fire during the Deepwater Horizon oil spill of 2010Fireboat response crews battling the blazing remnants of the offshore oil rig Deepwater Horizon in the Gulf of Mexico, April 21, 2010. [See all videos for this article](https://www.britannica.com/event/Deepwater-Horizon-oil-spill/images-videos) The Deepwater Horizon rig, owned and operated by offshore-oil-drilling company Transocean and leased by [oil](https://www.britannica.com/science/petroleum) company [BP](https://www.britannica.com/money/BP-PLC), was situated in the Macondo oil prospect in the Mississippi Canyon, a valley in the [continental shelf](https://www.britannica.com/science/continental-shelf). The oil well over which it was positioned was located on the seabed 4,993 feet (1,522 metres) below the surface and extended approximately 18,000 feet (5,486 metres) into the [rock](https://www.britannica.com/science/rock-geology). On the night of April 20 a surge of [natural gas](https://www.britannica.com/science/natural-gas) blasted through a [concrete](https://www.britannica.com/technology/concrete-building-material) core recently installed by contractor [Halliburton](https://www.britannica.com/money/Halliburton) in order to seal the well for later use. It later emerged through documents released by [Wikileaks](https://www.britannica.com/topic/WikiLeaks) that a similar incident had occurred on a BP-owned [rig](https://www.britannica.com/dictionary/rig) in the [Caspian Sea](https://www.britannica.com/place/Caspian-Sea) in September 2008. Both cores were likely too weak to withstand the pressure because they were composed of a [concrete](https://www.britannica.com/technology/concrete-building-material) mixture that used [nitrogen](https://www.britannica.com/science/nitrogen) gas to accelerate curing. Once released by the fracture of the core, the [natural gas](https://www.britannica.com/science/natural-gas) traveled up the Deepwater rig’s riser to the platform, where it ignited, killing 11 workers and injuring 17. The rig capsized and sank on the morning of April 22, rupturing the riser, through which [drilling mud](https://www.britannica.com/technology/drilling-mud) had been injected in order to counteract the upward [pressure](https://www.britannica.com/science/pressure) of oil and natural gas. Without any opposing [force](https://www.britannica.com/science/force-physics), oil began to [discharge](https://www.britannica.com/dictionary/discharge) into the gulf. The volume of oil escaping the damaged well—originally estimated by BP to be about 1,000 barrels per day—was thought by U.S. [government](https://www.britannica.com/topic/government) officials to have peaked at more than 60,000 barrels per day. ## Leaking oil Although [BP](https://www.britannica.com/money/BP-PLC) attempted to activate the rig’s blowout preventer (BOP), a fail-safe mechanism designed to close the channel through which oil was drawn, the device malfunctioned. [Forensic](https://www.merriam-webster.com/dictionary/Forensic) analysis of the BOP completed the following year determined that a set of massive blades known as blind shear rams—designed to slice through the pipe carrying oil—had malfunctioned because the pipe had bent under the pressure of the rising gas and oil. (A 2014 report by the U.S. Chemical Safety Board claimed that the blind shear rams had activated sooner than previously thought and may have actually punctured the pipe.) Efforts in May to place a containment dome over the largest leak in the broken riser were thwarted by the buoyant action of gas [hydrates](https://www.britannica.com/science/hydrate)—gas molecules in an ice matrix—formed by the reaction of natural gas and cold water. When an attempt to employ a “top kill,” whereby [drilling mud](https://www.britannica.com/technology/drilling-mud) was pumped into the well to stanch the flow of oil, also failed, BP in early June turned to an apparatus called the Lower Marine Riser Package (LMRP) cap. With the damaged riser shorn from the LMRP—the top segment of the BOP—the cap was lowered into place. Though fitted loosely over the BOP and allowing some oil to escape, the cap enabled BP to [siphon](https://www.britannica.com/technology/siphon-instrument) approximately 15,000 barrels of oil per day to a [tanker](https://www.britannica.com/technology/tanker). The addition of an [ancillary](https://www.merriam-webster.com/dictionary/ancillary) collection system [comprising](https://www.merriam-webster.com/dictionary/comprising) several devices, also tapped into the BOP, increased the collection rate to approximately 25,000 barrels of oil a day. [![Warm water fuels Hurricane Katrina. This image depicts a 3-day average of actual dea surface temperatures for the Caribbean Sea and Atlantic Ocean, from August 25-27, 2005.](https://cdn.britannica.com/49/93649-131-FB06761E/Satellite-image-sea-surface-temperatures-display-Hurricane-Aug-27-2005.jpg) Britannica Quiz Disasters of Historic Proportion](https://www.britannica.com/quiz/disasters-of-historic-proportion) In early July the LMRP cap was removed for several days so that a more permanent seal could be installed; this capping stack was in place by July 12. Though the leak had slowed, it was estimated by a government-commissioned panel of scientists that 4,900,000 barrels of oil had already leaked into the gulf. Only about 800,000 barrels had been captured. On August 3 BP conducted a “static kill,” a procedure in which drilling mud was pumped into the well through the [BOP](https://www.britannica.com/dictionary/BOP). Though similar to the failed top kill, mud could be injected at much lower pressures during the static kill because of the stabilizing influence of the capping stack. The defective BOP and the capping stack were removed in early September and replaced by a functioning BOP. The success of these procedures cleared the way for a “bottom kill,” considered to be the most likely means of permanently sealing the leak. This entailed pumping [cement](https://www.britannica.com/technology/cement-building-material) through a channel—known as a relief well—that paralleled and eventually intersected the original well. Construction of two such wells had begun in May. On September 17 the bottom kill maneuver was successfully executed through the first relief well. The second had been intended to serve as a [backup](https://www.britannica.com/dictionary/backup) and was not completed. Two days later, following a series of pressure tests, it was announced that the well was completely sealed. Quick Facts Also called: Gulf of Mexico oil spill Date: April 20, 2010 - September 19, 2010 (Anniversary in 4 days) Trusted knowledge for those who want to know more. [SUBSCRIBE](https://premium.britannica.com/premium-membership/?utm_source=premium&utm_medium=inline-cta&utm_campaign=shorter-2026) ![Penguin, ship, mountain, atlas](https://cdn.britannica.com/marketing/inline-left.webp) ![shohei ohtani, plants, andy wharhol art](https://cdn.britannica.com/marketing/inline-right.webp) ![Mobile](https://cdn.britannica.com/marketing/inline-mobile.webp?w=400) Claims by several research groups that subsurface plumes of dispersed [hydrocarbons](https://www.britannica.com/science/hydrocarbon) had been detected in May were initially dismissed by BP and the [National Oceanic and Atmospheric Administration](https://www.britannica.com/topic/National-Oceanic-and-Atmospheric-Administration) (NOAA). However, it was verified in June that the plumes were in fact from the Deepwater spill. The effect of the microscopic oil droplets on the ecosystem was unknown, though their presence, along with that of a layer of oil several inches thick discovered on portions of the seafloor in September, cast doubt on earlier [predictions](https://www.britannica.com/dictionary/predictions) about the speed with which the discharged oil would dissipate. [Bacteria](https://www.britannica.com/science/bacteria) that had adapted to consuming naturally occurring gas and oil seeping from the seabed were thought to have consumed a portion of it.
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