BP's top kill effort fails to plug Gulf oil leak -Live feed of the Gulf oil spill

ROBERT, La. - BP admitted defeat Saturday in its attempt to plug the Gulf of Mexico oil leak by pumping mud into a busted well, but said it's readying yet another approach to fight the spill after a series of failures.

BP PLC Chief Operating Officer Doug Suttles said the company determined the "top kill" had failed after it spent three days pumping heavy drilling mud into the crippled well 5,000 feet underwater. More than 1.2 million gallons of mud was used, but most of it escaped out of the damaged riser.

In the six weeks since the spill began, the company has failed in each attempt to stop the gusher, as estimates of how much is leaking grow more dire. It's the worst spill in U.S. history - exceeding even the Exxon Valdez disaster in 1989 off the Alaska coast - dumping between 18 million and 40 million gallons into the Gulf, according to government estimates.

"This scares everybody, the fact that we can't make this well stop flowing, the fact that we haven't succeeded so far," Suttles said. "Many of the things we're trying have been done on the surface before, but have never been tried at 5,000 feet."

The company failed in the days after the spill to use robot submarines to close valves on the massive blowout preventer atop the damaged well, then two weeks later ice-like crystals clogged a 100-ton box the company tried placing over the leak. Earlier this week, engineers removed a mile-long siphon tube after it sucked up a disappointing 900,000 gallons of oil from the gusher.

Suttles said BP is already preparing for the next attempt to stop the leak that began after the Deepwater Horizon drilling rig exploded in April, killing 11 people.

The company plans to use robot submarines to cut off the damaged riser from which the oil is leaking, and then try to cap it with a containment valve. The effort is expected to take between four and seven days.

"We're confident the job will work but obviously we can't guarantee success," Suttles said of the new plan, declining to handicap the likelihood it will work.

He said that cutting off the damaged riser isn't expected to cause the flow rate of leaking oil to increase significantly.

The permanent solution to the leak, a relief well currently being drilled, won't be ready until August, BP says.

Experts have said that a bend in the damaged riser likely was restricting the flow of oil somewhat, so slicing it off and installing a new containment valve is risky.

"If they can't get that valve on, things will get much worse," said Philip W. Johnson, an engineering professor at the University of Alabama.

Johnson said he thinks BP can succeed with the valve, but added: "It's a scary proposition."