Under-pressure oil group BP said the cost of cleaning up the mammoth spill in the Gulf of Mexico had hit around 760 million US dollars (£523 million) so far.
BP said it was too early to put a figure on the ultimate bill as lawsuits continue to flood in and as cash was pumped in to efforts to halt the leak and minimise the environmental toll.
The cost has soared by 135 million dollars (£93 million) in the past week alone.
So far, 23,000 claims have been filed and 9,000 have been paid, according to BP.
The group has made grants to the affected states of Florida, Alabama, Louisiana and Mississippi to help with their clean-up costs.
But oil is still spilling out at an estimated rate of around 5,000 barrels a day.
BP has been collecting oil from a mile-long siphon tube; however this is only capturing around 2,010 barrels a day on average - and as few as 1,360 barrels on some days.
The BP-operated Deepwater Horizon rig exploded and sank on April 20, killing 11 workers and causing an environmental disaster.
The group began drilling two relief wells earlier this month at around 13,000ft (3,962m) below the seabed in an attempt to cut off the flow of oil, but these are expected to take three months to complete.
In the meantime it is looking at so-called "top kill" plans to plug the well by injecting special fluids to stem the flow of oil, followed by cement to seal it.
Work is also continuing to try to disperse the huge oil slick which has reached the surface of the sea, with more than 1,100 boats and recovery vessels being used and nearly 2.5 million feet of boom.
US President Barack Obama has been piling the pressure on BP, accusing it of a "breakdown of responsibility" at the weekend as he announced a six-month investigation into the disaster.