Four years ago this month, BP's (NYSE: BP [FREE Stock Trend Analysis]) Deepwater Horizon oil rig exploded. The accident killed 11 people, injured 17 more and sent oil gushing into the Gulf of Mexico.
For three months, engineers struggled to stop the leak. When they finally succeeded, millions of barrels of oil had poured into the Gulf.
Today basic questions about the spill -- how big it was, the damage it caused and who has to pay whom -- still remain.