Last April 20, an explosion rocked the Deepwater Horizon oil-drilling rig – a platform the size of two football fields moored in the Gulf of Mexico. The rig, operated by energy giant BP, had just placed a temporary seal on the oil well it was drilling. A more permanent production platform was planned to extract the 50 million barrels of oil in the reservoir that workers had tapped 5,486 meters (18,000 feet) below the seafloor. One barrel equals 159 liters (42 gallons). But two days after the explosion, the fiery rig sank a mile to the bottom of the Gulf. Near the wreckage, broken pipes steadily leaked an estimated 35,000 to 60,000 barrels of oil per day from the underwater well.