— Deepwater Horizon, owned by Transocean Ltd. and leased to BP PLC, was a semi-submersible drilling rig, exploring for oil and natural gas.
— The structure that exploded Thursday, owned by Mariner Energy Inc., was a stationary platform, producing 58,800 gallons of oil and 900,000 cubic feet of gas per day from a proven reservoir using several wells.
— Deepwater Horizon was drilling in 5,000 feet of water in a deepwater region of the Gulf.
— The platform was operating in 340 feet of water in a shallow area of the Gulf known as a major source of gas.
— The Deepwater Horizon had 126 workers aboard at the time of the explosion.
— Mariner Energy's platform had 13 workers aboard Thursday.
— The Obama administration's six-month deepwater drilling moratorium shut down 33 drilling rigs in the Gulf.
— The moratorium did not affect the operations of the 3,400 production platforms in the Gulf, including the one owned by Mariner Energy.
— Deepwater Horizon had a blowout preventer that failed, unleashing 206 million gallons of crude into the Gulf before it was capped in July.
— Platforms generally have a series of redundant valves that can shut off oil and gas at different points along the pipeline that bring oil and gas to shore. Mariner Energy said the wells on its platform were shut down before the fire.
— London-based BP is one of the world's largest energy companies, not only producing oil and gas, but also producing refined products, such as gasoline and chemicals, and selling fuel through branded stations. Switzerland-based Transocean is the world's largest drilling contractor.
— Houston-based Mariner Energy is an independent petroleum producer, meaning it derives virtually all of its revenue from selling the oil and gas it produces. In April, Apache Corp., another independent oil company, announced plans to buy Mariner in a cash-and-stock deal valued at $3.9 billion, including the assumption of about $1.2 billion of Mariner's debt. That deal is pending.