Details of the largest criminal penalty in U.S. corporate history could emerge later today. British oil giant BP could face a record fine for the Deepwater Horizon oil spill in the Gulf of Mexico in 2010.

After months of haggling BP has apparently reached agreement with the Department of Justice and is set to plead guilty to criminal charges over the spill. Today we might learn the size of the fine. BP has set aside $3 billion.

But Nick McGregor, an oil analyst with stockbrokers Redmayne-Bentley says it will likely be much higher:

“The Department of Justice will draw enough blood from BP to make it very, very clear that this is not something that any other business ever wants to consider getting into.”

McGregor says BP could be fined as much as $21 billion. $10 or $12 billion is thought more likely but that would still be around ten times higher than the highest U.S. corporate fine on record.