Here is some background information on the Deepwater Horizon explosion and sinking causing a massive oil spill.
The Coast Guard began burning off the slick nearly a week after the rig sank in 5000 feet of water:
The burn began at 5 p.m. CDT (4/28), an agency spokesman said. Workboats were to pool segments of the spill inside a fire-resistant "boom," essentially a floating corral, to be towed to a remote area for burning, the Coast Guard said.
BP, which owns the well, is spending millions of dollars a day on what it has called the largest oil spill containment operation in history, involving dozens of ships and aircraft.
The agency said it planned "small, controlled burns" of several hundred gallons each lasting about an hour and invisible from shore.