The lawyers for British oil giant BP and the US federal government have disagreed over methods used to assess the size of the oil spill in the Gulf of Mexico following the 2010 Deepwater Horizon Disaster.

While the government estimates a total spill size of about 4.9 million barrels of oil, BP claims that just 3.26 million barrels escaped into the sea. A total of 810,000 barrels of oil collected during the cleanup is excluded from the spill size.

Government attorney Steve O'Rourke said the leakage was similar to an Exxon Valdez-type spill occurring about every 4.5 days for the duration of the incident. O'Rourke added that BP's estimate for the spill is well below the actual size as the company was emphasizing the lower end of its estimate.

Meanwhile, BP lawyer Mike Brock criticised government scientists' methods for calculating the spill. Brock argued that they committed a wide range of errors as they rushed to make an estimate shortly after the spill, in order to appease the public.

In the ongoing second phase of the multi-billion-dollar lawsuit, US District Judge Carl Barbier is assessing the total amount of oil spilled into the Gulf for 87 days. Earlier, he assessed BP's efforts to cap the Macondo well.

Rising Costs

An explosion on BP's Deepwater Horizon rig on 20 April 2010, which killed 11 workers, resulted in one of the worst environmental disasters in history. BP has since forked out $42.4bn (€31.4bn, £26.4bn) in oil spill related charges.

BP's costs are still mounting as it has taken a substantial hit in the running of the victims' settlement programme. This includes payments to court-appointed vendors and appeals panelists. It also has to bear administrative costs to process remaining claims from the Gulf Coast Claims Facility, a fund set up to pay claimants before the current settlement was reached.

The company originally expected the programme to cost $7.8bn, but recently it lifted its estimate to $9.6bn and said it could go higher due to excessive fees and false claims.

Earlier, BP's plea to reconsider some payments under the 2012 Gulf of Mexico disaster settlement programme was approved by a US federal appeals court. The verdict is a relief for the company trying to cut down its rising costs related to the oil spill.

In the second phase of the trial, the company may get additional fines up to $17bn under the US Clean Water Act, which provides for a maximum fine of $1,100 for each barrel of oil spilled.