Knotty Head was at one point the deepest oil well in the Gulf of Mexico. It is drilled in 3,500 ft (1,067 m) of water and 30,589 ft (9,324 m) below the sea floor. It is jointly owned by Chevron, Anadarko Petroleum Corporation, BHP Billiton and Nexen Inc. with each having 25% of the share. Initially, the well was estimated to hold 350 million to one billion barrels of oil, but additional tests have cut that estimate down to 200 million to 500 million.