BP PLC agreed to accept criminal responsibility for the 2010 Deepwater Horizon disaster that killed 11 workers and to pay $4.5 billion in fines and restitution, the biggest penalty ever levied by the U.S. Justice Department.

But the oil producer still faces an even costlier battle with the government over civil penalties for the pollution unleashed when the drilling rig exploded in the Gulf of Mexico and caused the worst offshore oil spill in U.S. history.

The oil damaged the region's important seafood and tourism industries, resulting in billions of dollars in lost revenue. For weeks, repeated efforts to stop the gushing crude failed, as underwater cameras sent the live images to TV viewers. Finally, almost three months later, the well was capped.

Under the agreement, BP said it will plead guilty to 11 felony counts of "seaman's manslaughter" relating to the deaths aboard the drilling rig, admitting that its workers were negligent when they misinterpreted a key well safety test.

The company also will plead guilty to one felony count of obstruction of Congress stemming from false information it gave about the rate that oil was leaking from the well.