The Gulf of Mexico oil blow-out may have been leaking twice as much as previously thought, scientists fear.
More than 100 million gallons may have already been released, affecting people and wildlife along the US coast from Louisiana to Florida.
It is the third time the US government has had to increase its estimate of the leak's size.
All the new estimates are worse than earlier ones - and far more costly for BP, which has seen its stock sink since the April 20 explosion that killed 11 workers and triggered the spill.
Most estimates had more oil flowing in an hour than what officials once said was spilling in an entire day.
"This is a nightmare that keeps getting worse every week," said Michael Brune of the US environmental pressure group the Sierra Club.
"We're finding out more and more information about the extent of the damage. ... Clearly we can't trust BP's estimates of how much oil is coming out."
The spill was flowing at a daily rate that could possibly have been as high as 2.1 million gallons, twice the highest number the federal government had been saying, US Geological Survey Director Marcia McNutt, who is co-ordinating estimates, said.
The estimate was for the flow before June 3 when a riser pipe was cut and then a cap placed on it. No estimates were given for the amount of oil gushing from the well after the cut, which BP said would increase the flow by about 20%. Nor are there estimates since a cap was put on the pipe, which already has collected more than three million gallons.
The estimates are not nearly complete and different teams have come up with different numbers. A new team from the Woods Hole Oceanographic Institute came in with even higher estimates, ranging from 1 million gallons a day to 2.1 million gallons. If the high end is true, that means nearly 107 million gallons have spilled since April 20.
Even using other numbers that federal officials and scientists call a more reasonable range would have about 63 million gallons spilling since the rig explosion.
By comparison, the worst peacetime oil spill, 1979's Ixtoc 1 in Mexico, was about 140 million gallons over 10 months.
The Gulf spill has not yet reached two months. The Exxon Valdez, the previous worst US oil spill, was about 11 million gallons and the new figures mean Deepwater Horizon is producing an Exxon Valdez size spill every five to 13 days.
Yesterday President Barack Obama consoled relatives of the 11 workers killed in the oil rig explosion, acknowledging their "unimaginable grief" and personally assuring the families he will stand with them.
Later the White House released a letter from Coast Guard Adm. Thad Allen, who is overseeing the crisis for the government, inviting BP Chairman Carl-Henric Svanberg and "any appropriate officials from BP" to meet senior administration officials.
As the crude continues to foul the water, Louisiana leaders are rushing to the defence of the oil-and-gas industry and pleading with Washington to immediately bring back offshore drilling.
Although angry at BP over the disaster, state officials warn that the Obama administration's six-month halt to new permits for deep-sea oil drilling has sent Louisiana's most lucrative industry into a death spiral.