Top-kill plan will see BP use mud to tame oil leak

The Coast Guard said it gave the approval for the "top kill" manoeuvre after consulting with government scientists. The technique has never before been tried a mile beneath the sea, and BP officials said it could be days before they know whether it is working. Engineers were hoping to pump enough mud into the gusher to stem the flow then pour in cement to seal the well.

Millions of gallons of oil has spewed into the ocean since an 20 April rig explosion.

Meanwhile, newly released Coast Guard witness statements show senior managers complained that oil giant BP was "taking shortcuts" by replacing heavy drilling fluid with saltwater in the well that blew out.

Truitt Crawford, a roustabout for drilling rig owner Transocean, told Coast Guard investigators about the complaints. The seawater, which would have provided less weight to contain a surge in pressure, 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," Mr Crawford said in his statement.

A spokesman for BP, which was leasing the Deepwater Horizon rig when it exploded, killing 11 workers and triggering a massive oil spill in the Gulf of Mexico, refused to comment.

Meanwhile, 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 build-up of pressure that was an "indicator of a very large abnormality," BP's investigator said, according to the memo.

However, the rig team were "satisfied" another test was successful and resumed adding the seawater, said the memo by US Representatives 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 an emergency. BP has said its failure contributed 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 Transocean chief mate left two crew members to deal with the issue on their own.

However, what at first appeared routine, suddenly turned to panic. The workers called bosses to report a situation, with assistant driller Stephen Curtis telling one senior operator the well was "coming in". Someone told well site leader Donald Vidrine they were "getting mud back".

The toolpusher, Jason Anderson, tried to shut down the well. However, this did not work. Both Mr Curtis and Mr Anderson died in the explosion.

At least seven million gallons of crude has spilled into the sea since, fouling Louisiana's marshes and coating birds and other wildlife, fuelling growing frustration with BP and the federal government.