BP General Counsel Rupert Bondy said BP is ready to face a federal trial Monday in the U.S. District Court for the Eastern District of Louisiana.
A two-phase trial in New Orleans will determine responsibility for the Deepwater Horizon disaster and the amount of fines for alleged violations of the Clean Water Act. Eleven rig workers died when the Deepwater Horizon rig exploded and sank, leading to the worst offshore accidental oil spill in world history.
BP said the government estimate of 4.9 million barrels of oil spilled, however, was too high.
"These issues are extremely complicated as a technical matter and there is still further analysis to do," said Bondy. "But it is clear, based on our analysis so far, that the government's public estimate is simply wrong and overstated by at least 20 percent."
The U.S. court in Louisiana last month accepted a guilty plea from BP that resolves "all federal criminal charges" against the company for the 2010 oil spill in the Gulf of Mexico.
BP in November agreed to plead guilty to 14 criminal charges stemming from the accident as well as to $4 billion in fines and penalties.