The amount estimated by the company that it needs to compensate individuals and businesses has been increased from 8.2 billion US dollars (£5.3 billion) to 9.6 billion US dollars (£6.3 billion). It was previously 7.8 US billion dollars (£5.1 billion).
It means that just 300 million US dollars (£196 million) is left of a 20 billion US dollar (£13 billion) trust fund set up by the company to settle its legal obligations following the disaster.
BP said it continued to dispute a court interpretation of the US settlement agreement it signed following the 2010 disaster in the Gulf of Mexico - which it has argued allows businesses to claim for non-existent losses.
Its total estimated bill following the disaster now stands at 42.4 billion US dollars (£27.7 billion), which also includes clean-up costs and fines.
Costs are being paid out of the 20 billion US dollars trust fund set up following the catastrophe, but the latest figures show 19.7 billion US dollars (£12.8 billion) of this have now been used up.
The company disclosed the new figure as it published financial results for the second quarter of the year, which showed profits down sharply to 2.7 billion US dollars (£1.8 billion).
The 25% decline compared with the same period last year was blamed on lower oil prices and a higher tax bill.
BP said the increase in the Deepwater Horizon settlement comprised 900 million US dollars (£590 million) to reflect additional notices for claims received and 500 million US dollars (£330 million) for extra claims administration costs.
It has taken its dispute over the the way the settlement is being handled - by a court-appointed claims administrator and judge - to the US appeals court, arguing that it is the victim of "fictitious and inflated" compensation claims which threaten its future. BP is awaiting the court's decision.
The oil giant alleges that the handling of the settlement has sparked a "feeding frenzy" and is allowing businesses from the Gulf coast to claim for "non-existent, artificially calculated losses".
The blow-out of the Deepwater Horizon well off the Louisiana coast in 2010 claimed 11 lives and damaged fishing and tourism industries as well as marine and wildlife habitats, forcing BP to agree a multi-billion compensation deal in April 2012.
But it has warned in court filings that it will be "irreparably harmed" unless the compensation system is reformed, saying the cash drain could put its dividend at risk and make it vulnerable to a takeover.
Elsewhere in today's announcement, BP chief executive Bob Dudley said there had a been a strong underlying pre-tax performance from its businesses, with growth in production from new projects and good progress in exploration.