The new figure supports what many observers have assumed from the images of oil slicking the gulf surface, slathering beaches and spurting from a pipe on the sea floor: This is the worst oil spill in U.S. history.
President Obama, feeling pressure to act in a crisis now in its sixth week, yanked the exploratory drilling permits for 33 deepwater rigs in the gulf and suspended planned exploration in two areas off the coast of Alaska. He announced the moves at a news conference carried on cable TV channels that simultaneously showed the live video feed of effluent billowing from the cracked riser pipe at the bottom of the gulf.
Obama pushed back on suggestions that, as he put it, "BP is off running around doing whatever it wants and nobody is minding the store." He said that his administration is doing all it can, but that, when it comes to plugging the leak, "the federal government does not possess superior technology to BP."
The eventful day included the first prominent administrative casualty of the crisis. Elizabeth Birnbaum, head of Minerals Management Service, which issues permits for offshore drilling, resigned.
The political developments continue to be overshadowed by a technological struggle that has no precedent. Whether the top kill is going to work remains highly uncertain.
The maneuver is a brute-force, yet delicately calibrated, injection of heavy drilling mud into the blowout preventer atop the wellhead. As the mud is pumped from ships at the surface, the hydrocarbons should be forced back down the well toward their source in a porous reservoir called the Macondo field, about 2 1/2 miles below the floor of the gulf.
It has not been smooth sailing. After pumping mud for about nine hours on Wednesday, BP put the pumping on hold throughout the day Thursday while it pondered the initial results. The company resumed Thursday evening.
"Nothing has gone wrong or unanticipated," Doug Suttles, BP's chief operating officer, told reporters. He said engineers hope to improve on their initial performance by preceding a mud injection with a blast of rubber balls and other rough-textured materials -- a "junk shot" -- to clog the blowout preventer and force more mud down into the hole, rather than shooting it out of the leaks in the riser.
"We did believe we did pump some mud down the well bore. We obviously pumped a lot of mud out the riser," Suttles said.
BP Managing Director Bob Dudley likened the top kill to an "arm-wrestling match with two fairly equal-rated forces. Or taking two fire hoses and driving them together, trying to overcome the other."
The well won't be considered killed until the mud injection has been followed by cement to permanently plug it -- at which point the news would be carried by "the roar coming out of this building," the deadpan Suttles said.