BP has said more oil than the 5,000 barrels a day it initially estimated is flowing from a burst oil well into the Gulf of Mexico.
The energy giant said a long tube it inserted into the gusher at the weekend was now siphoning 5,000 barrels a day, but that more was escaping.
Meanwhile, US officials have ordered BP to use a less toxic chemical to disperse the crude.
The spill has reached Louisiana and is now threatening Florida and Cuba.
Oil has been gushing since the offshore drilling rig Deepwater Horizon, leased by BP, exploded off the coast of Louisiana on 20 April and sank two days later.
'A little more'
BP had stuck by its first estimate that some 5,000 barrels, or 210,000 gallons, a day of crude was leaking from the well - despite claims from several experts that the figure was at least 10 times higher.
But BP spokesman Mark Proegler told news agency AFP on Thursday: "Now that we are collecting 5,000 barrels a day, it might be a little more than that."
A live video feed that shows the oil gushing from the well has been made available by BP after pressure from a US congressman.
It shows a large, flowing plume of oil and gas next to the tube that is carrying some of it to the surface.
Mr Proegler continued: "We said from the beginning, our experts have been saying there really is no reliable way to estimate the flow from the riser."
The oil firm's temporary solution has been to funnel the oil up to a ship, but on Sunday it is preparing its latest attempt to seal the rupture.
Engineers are planning a so-called "top kill" operation, in which heavy mud would be injected to stem the oil flow, then cement used to block the well permanently.
The procedure has worked before to stop oil gushing above ground, but like other methods BP is exploring, it has never been used a mile below the sea, where the well is located.
The US Environmental Protection Agency (EPA) has told BP to use a new dispersant to contain the oil spill, as fears grow about potential damage from the use of such chemicals.
BP has used a number of dispersants, all approved by the EPA, to try to break up the crude.
Outrage from environmentalists over the ballooning slick - which is visible from space - has been mounting.
Greenpeace campaigners scaled the London headquarters of BP on Thursday and unfurled a flag with BP's logo and the words "British Polluters".
It emerged on Wednesday a small portion of the slick had entered the so-called Loop Current, which could take it to Florida and up the eastern US coast.
Florida's state meteorologist said it would be at least a week before the oil reached waters near the state.
Farther south, US officials have been talking to Cuba about how to respond should the spill reach the island's northern coast, said a US state department spokesman.