BP says it is trying to seal the blown-out oil well in the Gulf of Mexico by pumping heavy mud into it.
BP said in a news release Wednesday that the "top kill" maneuver has started. The top kill has never before been tried a mile beneath the sea, and company officials say it could be a couple of days before they know whether it is working.
Engineers hope to pump enough mud into the gusher to overcome the flow of the well. Engineers plan to follow up the mud with cement that the company hopes will permanently seal the well.
BP's top executive has pegged the top kill's chance of success at 60 to 70 percent.
Millions of gallons of oil has spewed into the ocean since an April 20 rig explosion.
THIS IS A BREAKING NEWS UPDATE. Check back soon for further information. AP's earlier story is below.
COVINGTON, La. (AP) -- Senior managers complained oil giant BP was "taking shortcuts" by replacing heavy drilling fluid with saltwater in the well that blew out, triggering the massive oil spill in the Gulf of Mexico, according to witness statements obtained by The Associated Press.
Truitt Crawford, a roustabout for drilling rig owner Transocean Ltd., told Coast Guard investigators about the complaints. The seawater, which would have provided less weight to contain surging pressure from the ocean depths, was being used to prepare for dropping a final blob of cement into the well.
"I overheard upper management talking saying that BP was taking shortcuts by displacing the well with saltwater instead of mud without sealing the well with cement plugs, this is why it blew out," Crawford said in his statement.
A spokesman for BP, which was leasing the rig Deepwater Horizon when it exploded April 20, killing 11 workers and triggering a massive oil spill in the Gulf of Mexico, declined to comment.
The Coast Guard on Wednesday granted final approval for BP's latest bid to plug the leaking well by force-feeding it heavy drilling mud and cement. There was no word on when that attempt might begin.
President Barack Obama cautioned that there was no guarantee the attempt known as a top kill would work. He said Wednesday that the "heartbreaking" spill underscores the urgent need for alternative fuel sources to feed the United States' energy needs.
At a company in northern California that makes solar panels, Obama noted the danger of drilling deep offshore.
"With the increased risks, the increased costs -- it gives you a sense of where we're going," Obama said. "We're not going to be able to sustain this kind of fossil fuel use. This planet can't sustain it."
Meanwhile, the statements from workers ahead of a hearing in New Orleans on Wednesday and a congressional memo about a BP internal investigation of the blast indicated warning signs were ignored. Tests less than an hour before the well blew out found a buildup of pressure that was an "indicator of a very large abnormality," BP's investigator said, according to the congressional memo.
Still, the rig team was "satisfied" that another test was successful and resumed adding the seawater, said the memo by U.S. Reps. Henry Waxman and Bart Stupak to members of the Committee on Energy and Commerce, which is investigating what went wrong.
There were other signs of problems, including an unexpected loss of fluid from a pipe known as a riser five hours before the explosion, which the memo said could have indicated a leak in the blowout preventer, a huge piece of equipment that should have shut down the well in case of an emergency. BP has cited its failure as a contributor to the blast.
The witness statements show rig workers talked just minutes before the blowout about pressure problems in the well. At first, nobody seemed too worried: The chief mate for Transocean left two crew members to deal with the issue on their own.
What began as a routine pressure problem, however, suddenly turned to panic. The workers called bosses to report a situation, with assistant driller Stephen Curtis telling one senior operator that the well was "coming in." Someone told well site leader Donald Vidrine that they were "getting mud back." The toolpusher, Jason Anderson, tried to shut down the well.
It didn't work. Both Curtis and Anderson died in the explosion.
At the hearing in New Orleans on Wednesday, Douglas Brown, the Deepwater Horizon's chief mechanic, testified about what he described as a "skirmish" between someone he called the "company man" -- a BP official -- and three other employees during a meeting the day of the explosion.
Brown said he didn't pay particular attention to what they were discussing because it did not involve his engine room duties. He later said he did not know the BP official's name.
"The driller outlined what would be taking place, but the company man stood up and said 'We'll be having some changes to that,'" Brown testified. He said the three other workers initially disagreed but "the company man said 'This is how it's going to be.'"
Frustration with BP and the federal government has only grown since then as efforts to stop the leak have failed. At least 7 million gallons of crude have spilled into the sea, fouling Louisiana's marshes and coating birds and other wildlife.
Obama prepared to head to the Gulf on Friday to review efforts to halt the oil that scientists said seems to be growing significantly darker, from what they can see in an underwater video. It suggests that heavier, more-polluting oil is spewing out.
Ahead of his trip, Obama planned to address an Interior Department review of offshore drilling that is expected to recommend tougher safety protocols and inspections for the industry, according to an administration official. The official spoke on condition of anonymity ahead of the public release Thursday of the findings of a 30-day review Obama ordered after the spill.
A new report from the Interior Department's acting inspector general alleged that drilling regulators have been so close to oil and gas companies they've been accepting gifts including hunting and fishing trips and even negotiating to go work for them.
The top kill BP was poised to try Wednesday involves pumping enough mud into the gusher to overcome the flow of the well.
Engineers plan to follow it up with cement that the company hopes will permanently seal the well. It may be several days before BP knows if it worked. BP Chief Executive Tony Hayward earlier pegged its chances of success at 60 to 70 percent.
Bob Bea, an engineering professor at the University of California at Berkeley, said the procedure carries a high risk of failure because of the velocity at which the oil may be spewing.
"I certainly pray that it works, because if it doesn't there's this long waiting time" before BP can dig relief wells that would cut off the flow, Bea said.
Associated Press writers Mike Kunzelman in New Orleans, Jeff Donn in Boston, Ben Evans, Ben Feller, Fred Frommer and Erica Werner in Washington, Alan Sayre in Kenner, La., Curt Anderson in and Holbrook Mohr in Jackson, Miss., contributed to this story.