The Deepwater Horizon accident Deepwater Horizon oil spill, also called Gulf of Mexico 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. About 1,300 miles (2,100 km) of the U.S. Gulf Coast covered in oil. Massive harm done to wildlife in and around the Gulf of Mexico, including the deaths of an estimated 800,000 birds and 65,000 turtles. Release of an estimated 134 million to 206 million gallons of oil into the Gulf of Mexico. As much as 20 percent of the oil spilled may have sunk to the bottom of the ocean, damaging deep-sea ecosystems. 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 w