ROBERT, La. – The chief executive of BP PLC says it will be about 48 hours before they know if pumping heavy mud into a blown-out well is successful in stopping the massive Gulf of Mexico oil spill.
CEO Tony Hayward said on the CBS "Early Show" that his confidence level in the well-plugging bid remains at about 60 to 70 percent.
BP, the largest oil and gas producer in the United States, began injecting mud into the well on Wednesday afternoon in an untested bid to end a spill that has surpassed the Exxon Valdez disaster since it started after an oil rig explosion April 20 that killed 11 workers.
The maneuver, called a top kill, has worked on land but never been tried in deep water.
As the world waited, President Barack Obama announced major new restrictions on drilling projects, and the head of the federal agency that regulates the industry resigned under pressure, becoming the highest-ranking political casualty of the crisis so far.
Obama was scheduled to attend a briefing Friday at the U.S. Coast Guard Station in Grand Isle, La., by Adm. Thad Allen, who is overseeing the response to the spill. It would be his second visit to the region since the disaster began.
At the White House on Thursday, Obama acknowledged that his administration could have done a better job dealing with the spill and that it misjudged the industry's ability to handle a worst-case scenario.
"I take responsibility. It is my job to make sure that everything is done to shut this down," Obama said at a news conference, where he announced a series of new restrictions on oil drilling projects.
Hayward said on CBS that things were progressing as planned. He said BP engineers had completed a second phase by pumping what he called "loss prevention material" into the blowout preventer, a massive piece of machinery that sits atop the well. That material was supposed to form "a bridge against which we could pump" more heavyweight mud inside the blowout preventer.
That part of the operation was completed early Friday and appeared to have been partially successful. BP would go back to pumping more mud later Friday, he said.
If the mud works, BP would pour cement to seal the well.
"Clearly I'm as anxious as everyone in America is to get this thing done," Hayward said.
The stakes were higher than ever as public frustration over the spill grew and a team of government scientists said the oil has been flowing at a rate 2 1/2 to five times higher than what BP and the Coast Guard previously estimated.
Two teams of scientists calculated the well has been spewing between 504,000 and more than a million gallons a day. Even using the most conservative estimate, that means about 18 million gallons have spilled so far. In the worst-case scenario, 39 million gallons have leaked.
That larger figure would be nearly four times the size of the Exxon Valdez disaster, in which a tanker ran aground in Alaska in 1989, spilling nearly 11 million gallons.
The spill is not the biggest ever in the Gulf. In 1979, a drilling rig in Mexican waters — the Ixtoc I — blew up, releasing 140 million gallons of oil.
Associated Press Writers Seth Borenstein, Matthew Brown, Jason Dearen, Andrew Taylor and Matthew Daly contributed to this report.