BP said its "static kill" procedure, in which heavy drilling mud was used to push oil from the runaway well back into the reservoir, had been a success. It described the development as a "significant milestone."
The U.K. oil major may now move to seal the well for good by cementing it shut, if it gets the go-ahead from government scientists and officials. But the company has stressed that the only permanent solution to the spill is a relief well, which will be completed by the middle of this month.
Addressing industry officials at a public forum in New Orleans, Michael Bromwich, director of the Bureau of Ocean Energy Management—the government's new offshore-drilling oversight agency—said the apparent success of the static kill procedure was "a major achievement that we're all extremely pleased about."
But he added that there was still "much work to be done" by the oil industry to assure the administration and the public that deepwater drilling can resume safely in U.S. waters. The government has imposed a moratorium on deepwater drilling that is scheduled to last until Nov. 30.
Meanwhile, Carol Browner, energy and climate change adviser to President Barack Obama, said on a U.S. television talk show that "the vast majority of the oil appears to be gone." She said scientists had ascertained that about 75% of the oil had either evaporated or been broken down in the Gulf, or been captured or burned off.
She said "Mother Nature will continue to break it down," although some of it could continue to wash up onshore in the form of tarballs.
The success of the static kill marks a breakthrough in BP's attempts to subdue a well that the government estimates has spewed nearly five million barrels of crude into the Gulf of Mexico.
It comes more than three months after the Deepwater Horizon drilling rig exploded off the coast of Louisiana, killing 11 men and triggering what has now been acknowledged as the world's worst accidental oil spill at sea.