U.K.-listed oil and gas giant BP PLC (BP) said Tuesday it will defend itself vigorously in court next week against claims from the U.S. government for fines related to the Deepwater Horizon oil spill, which the company described as "excessive and not based on reality."

The company said it believes the
U.S. government's estimate that 4.9 million barrels of oil were spilled in the Gulf of Mexico during the incident is overstated by at least 20% and includes another 810,000 barrels of oil that BP captured from the leaking well, so never made contact with the environment.

"BP believes that a figure of 3.1 million barrels should be the uppermost limit of the number of barrels spilled that should be used in calculating a Clean Water Act penalty," the company said in a statement. "The U.S. Department of Justice has indicated that it agrees with BP's position on this issue."

BP added that it expects to be fined less than the statutory maximum under the Clean Water Act of $1,100 per barrel spilled, or $4,300 per barrel if the company were to be proved grossly negligent in its actions prior to the spill. "We firmly believe we were not grossly negligent," BP said.