The Deepwater Horizon oil spill (also referred to as the BP oil spill) began on April 20, 2010, in the Gulf of Mexico. Killing eleven people, it is considered the largest marine oil spill in the history of the petroleum industry and estimated to be 8% to 31% larger in volume than the previous largest, the Ixtoc I oil spill. Itoxic I was an exploratory well being drilled at the time. The US Government estimated the total discharge at 4.9 million barrels (210 million US gal; 780,000 m3). After several failed efforts to contain the flow, the well was declared sealed on September 19, 2010.

In October 2012, BP reported that they had found and plugged leaking oil from the failed containment dome, now abandoned about 1,500 feet (460 m) from the main well. In December 2012, the USCG conducted a subsea survey; no oil coming from the wells or the wreckage was found and its source remains unknown. In addition, white, milky substance was observed seeping from the wreckage. According to BP and the USCG, it is "not oil and it's not harmful."

In January 2013, BP said that they were continuing to investigate possible sources of the oil sheen. Chemical data implied that the substance might be residual oil leaking from the wreckage. If that proves to be the case, the sheen can be expected to eventually disappear. The oil slick was comparable in size to naturally occurring oil seeps and was not large enough to pose an immediate threat to wildlife.

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