The London-based oil giant estimated last year that it would spend roughly $7.8 billion to resolve tens of thousands of claims covered by the settlement agreement. But in a regulatory filing this week, BP PLC said businesses' claims have been paid at much higher average amounts than it had anticipated.

The company also said it can't reliably estimate how much it will pay for unresolved business claims following a ruling Tuesday by the federal judge supervising the uncapped settlement. U.S District Judge Carl Barbier rejected BP's interpretation of certain settlement provisions.

Barbier upheld claims administrator Patrick Juneau's interpretation of settlement terms that govern how businesses' pre- and post-spill revenue and expenses — and the time periods for those dollar amounts — are used to calculate their awards.

BP had argued that Juneau's interpretation would lead to "absurd results" and "false positives," but the judge said the settlement agreement anticipated that "such results would sometimes occur."

"Objective formulas, the possibility of 'false positives,' and giving claimants flexibility to choose the most favorable time periods are all consequences BP accepted when it decided to buy peace through a global, class-wide resolution," Barbier wrote.

BP spokesman Geoff Morrell said the company believes the way Juneau is processing business economic loss claims is "contrary to the agreement."

"His approach has produced unjustified windfall payments to numerous business claimants," Morrell said in a statement, adding that BP will pursue "all available legal options" to challenge Barbier's decision.

BP already had revised its estimate for the total cost of the settlement before Barbier's ruling, saying earlier this year that it expected to pay $8.5 billion instead of the $7.8 billion it estimated when it first cut the deal.

In this week's regulatory filing, the company said it has been analyzing the processing of recent claims to determine if they can be used to predict future claims, but concluded it can't.

Excluding business claims that Juneau hasn't received or processed yet, the company now estimates it will pay $7.7 billion to resolve the rest of the claims covered by the settlement.

"If BP is successful in its challenge to the court's ruling, the total estimated cost of the settlement agreement will, nevertheless, be significantly higher than the current estimate of $7.7 billion because business economic loss claims not yet received or processed are not reflected in the current estimate and the average payments per claim determined so far are higher than anticipated," the company said.

Barbier also is presiding over a non-jury trial designed to determine the causes of BP's April 2010 well blowout and assign percentages of fault to the companies involved in the disaster, which killed 11 workers and spawned the nation's worst offshore oil spill.

The trial, which opened Feb. 25 and is scheduled to resume Monday, could last several months if BP doesn't settle separate claims by the federal government and Gulf states over environmental and economic damage from the spill.