GuLF Study Environmental Health Sciences (NIEHS), part of the National Institutes of Health, and aims to recruit 55,000 of the 150,000 workers who volunteered or were employed to help clean up the spill. It is led by Dale Sandler, head of the NIEHS's epidemiology branch. The "Deepwater Horizon" oil spill was the world's largest accidental marine oil spill. It began on 20 April 2010 after an explosion on the "Deepwater Horizon", a drilling rig leased by BP to drill an exploratory well. Between then and 15 July, when the well was capped, over four million barrels of oil (around 170 million US
Offshore oil and gas in the Gulf of Mexico (United States) blowout) began on April 20, 2010, in the Gulf of Mexico on the BP-operated Macondo Prospect. 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. In 2012, federal leases in the Gulf of Mexico produced of oil, which made up 19.5% of all U.S. oil production that year, and more than that of any U.S. state other than Texas. The 2012 production was less than the in 2009; however, due to new