The "top kill" procedure has not stopped the largest oil spill in U.S. history, BP has conceded Saturday, as the company prepares yet another method to stop the flow of crude into the Gulf of Mexico.
After three days of shooting dense mud into the broken oil well 5,000 metres below the sea, BP's chief operating officer Doug Suttles said Saturday afternoon that the top hat method had failed.
The oil spill, which began several weeks ago, has sent between 68 million and 151 million litres of crude into the Gulf, making it the largest such spill in U.S. history.
BP has attempted a number of methods of plugging the broken well, which is polluting the Gulf's waters, its wildlife and coastal areas.
The company had calculated the odds of success at between 60 and 70 per cent for the top kill procedure, which had never been attempted at a depth of 5,000 metres.
Under BP's next plan, the company will attempt to cap the leaking well using a containment valve.
"We're confident the job will work but obviously we can't guarantee success," Suttles said of the company's next attempt.
U.S. President Barack Obama called the ongoing stream of oil into the Gulf "as enraging as it is heartbreaking."
The spill began last month after the Deepwater Horizon drilling rig exploded, killing 11 people and rupturing the pipe leading from its undersea well, far below the rig. It's the worst spill in U.S. history, dumping between 18 million and 40 million gallons into the Gulf.
Suttles said earlier on Saturday that the equipment necessary to try to put another cap on the leaking well or to replace the blowout preventer on the sea floor is already in place.
"That equipment is on station and ready to go and we've been prepping that all along in case we need to move to that option."
Defending the response
Suttles bristled at suggestions that BP has been trying to minimize the effects of the spill or evade responsibility for what even the company has now conceded is an environmental catastrophe.
"Since Day 2, when the rig sank, and Day 3 when we discovered the first leak on the seabed, we've been trying to stop this leak. We've been trying to do that," Suttles said.
Americans have been transfixed by the spill, watching an Internet "spillcam" showing the view from the bottom of the ocean with oil billowing out into the water in clouds.
BP says the only permanent solution is to drill a relief well, but that won't be completed until August.
The crisis, and the public response to the massive spill, drew Obama to parts of the Gulf coast affected by the spill. On Friday, Obama toured oil-tainted beaches to see the damage and to emphasize that his administration was in control of the 40-day crisis.
"I'm here to tell you that you are not alone, you will not be abandoned, you will not be left behind," he told people in Grand Isle, La., where the beach has been closed by gobs of oil and the frustration and anger are palpable.
The top kill operation began Wednesday, with BP pumping heavy drilling mud into the blown-out well in an effort to choke off the source of the spill, which has released far more than the 1989 Exxon Valdez disaster did off the Alaska coast.
Suttles said that as well as mud, the company also shot in assorted junk, including metal pieces and rubber balls to help to counter pressure from the well.
BP, under pressure from Congress, made available a live video feed of what is going on underwater, and about 3,000 websites were showing a version of it.
Environmental concerns grow
Meanwhile, environmental groups say they're quite worried about what the full impact of the spill will mean for wildlife in the Gulf. But they don't yet have a clear picture of how it is affecting animals that inhabit the area.
"What we do know is that in the last few weeks they've had over 300 seabirds, 19 dolphins and then 200 turtles wash up on shore dead," said Craig Stewart with WWF Canada. "They're trying to get a sense of what is killing these animals."
"Because this rig is 80 kilometres off shore, it is difficult to get a sense of how many wildlife are actually perishing in the area, especially seabirds that feed way out to sea," he added.
"We've never experienced anything like this. They have no idea what the long-term impacts are and what it's doing to the wildlife down there."
With files from The Associated Press
