BP temporarily halted its attempt to plug the Gulf of Mexico oil leak last night, saying it wanted to monitor the effects of the “top kill” attempt.
The oil giant said nothing was going wrong with the procedure, which involves force-feeding mud into the blown-out well in an attempt to overcome the oil flowing upward.
BP hoped to resume shooting mud into the well overnight.
Chief operating officer Doug Suttles said he was not surprised it was taking longer than expected.
The top kill has never been tried at 5,000ft underwater.
Meanwhile new US Government estimates show the Gulf disaster has easily eclipsed the Exxon Valdez as the biggest oil spill in American history.
A team of scientists trying to determine how much oil has been flowing since the offshore rig Deepwater Horizon exploded on April 20 and sank two days later found the rate was more than twice and possibly up to five times as high as previously thought.
The fallout from the spill has stretched all the way to Washington, where the head of the federal agency which oversees offshore drilling resigned yesterday and President Barack Obama insisted his administration, not BP, was calling the shots.
His comments marked a change in emphasis from earlier administration assertions that the government was overseeing the operation.
As for the spill, even using the most conservative estimate, the leak has grown to nearly 18million gallons over the past five weeks. In the worst-case scenario, 39million gallons may have spilled.
When the Exxon Valdez ran aground in Alaska in 1989, it spilled nearly 11million gallons.
“Now we know the true scale of the monster we are fighting in the Gulf,” said Jeremy Symons, vice-president of the National Wildlife Federation. “BP has unleashed an unstoppable force of appalling proportions.”
BP and the US Coast Guard estimated soon after the explosion that about 210,000 gallons a day was leaking, but scientists who watched underwater footage of the well had been saying for weeks that it was probably more.
US Geological Survey director Marcia McNutt said two different teams of scientists calculated the well has been spewing between 504,000 gallons and more than 1million gallons a day.
BP spokesman Steve Rinehart said the previous estimate came from industry experts and scientists based on the best data available at the time. Asked for the company’s response to the new numbers, he replied: “It does not and will not change the response. We are going all out on our response.”
Marine scientists also said they had discovered a massive new plume of what they believe to be oil deep beneath the Gulf, stretching 22 miles from the leaking wellhead north-east towards Mobile Bay, Alabama.
The discovery by researchers on the University of South Florida College of Marine Science’s Weatherbird II vessel is the second significant undersea plume recorded since the rig exploded.
Last week, BP inserted a mile-long tube to siphon some of the oil from the gushing well into a tanker. It sucked up 924,000 gallons, but engineers had to dismantle it so they could start the risky procedure known as a top kill to try to cut off the flow altogether by shooting heavy drilling fluid into the well.
If that works, BP will inject cement into the well to seal it. BP pegged its chance of success at 60% to 70% and Mr Obama warned that it “offers no guarantee of success”.
Lieutenant Commander Tony Russell, an aide to coastguard Admiral Thad Allen, said yesterday that the mud was stopping some oil and gas but had a way to go before it proved successful. The top kill started on Wednesday night.
In Washington, meanwhile, Minerals Management Service director Elizabeth Birnbaum stepped down from the job she has held since July 2009. Her agency has come under withering criticism from politicians of both parties over lax oversight of drilling and cosy ties with industry.
Polls show the public is souring on the administration’s handling of the catastrophe, and Mr Obama sought to assure Americans that the government was in control.
“I take responsibility. It is my job to make sure this thing is shut down,” he said at a White House news conference.
He announced that a new moratorium on drilling permits would be extended for six months.
He also said he was suspending planned exploration drilling off the coasts of Alaska and Virginia and on 33 wells currently being drilled in the Gulf of Mexico.