The US Coast estimates that as much as 39 million gallons of oil has leaked into the Gulf of Mexico since an offshore oil rig exploded April 20.

The BP oil spill is now the worst in U.S. history.

The busted deep sea well is spewing crude into the Gulf of Mexico at least four times faster than BP estimated; officials say 450,000 to 750,000 barrels have been spilled.

By comparison, the Exxon Valdez tanker spilled 257,000 barrels of oil into Alaska's Prince William Sound in 1989. 

The new estimate is that between 18 million gallons and a worst-case 39 million gallons of oil have fouled the gulf since the April 20 rig explosion. 

"This is obviously a very significant disaster," said Marcia McNutt, director of the U.S. Geological Survey.

The news came as BP's last-ditch "top kill" attempt to choke the gushing well with heavy mud made some halting progress, and then stalled. 

The mud stopped the oil flow for several hours, but it restarted as soon as the mud stopped pumping, BP honcho Doug Suttles said.

The company said things were going according to plan and that it would resume pumping mud overnight. The goal is to slow the oil flow enough to allow engineers to cap the well with cement. 

"It's a work in progress. We need to let it play itself out," said Coast Guard Adm. Thad Allen, who is in charge of the scene and who said he was cautiously optimistic. 

Officials said they hope to know today if the procedure, which has never been tried at such depths, was a success. 

In Washington, another head rolled: Elizabeth Birnbaum, the head of the Minerals Management Service, which oversees oil drilling, was forced to step down. 

The Interior Department agency has long been criticized by environmentalists as too cozy with Big Oil. In 2008, its regulators were caught in bed with energy lobbyists - literally - trading drugs and sexual favors.

BP had estimated the flow at 5,000 barrels a day. The USGS said it's really between 12,000 and 19,000 barrels - and possibly as much as 25,000 barrels per day.

Suttles said the 5,000-barrel estimate was always iffy and said the amount of the flow had no bearing on the firm's efforts to stop it. 

"I don't believe that at any time we have misled anyone on this," he said. 

A new Gallup poll showed the spill has dramatically changed American attitudes about the environment. 

Americans have shifted starkly from giving a slightly higher priority to energy production over environmental concerns last month to strongly backing the environment over energy this month.

Read more: http://www.nydailynews.com/news/national/2010/05/27/2010-05-27_gulf_oil_spill_the_worst_in_us_history_coast_guard_reports_surpassing_exxon_vald.html#ixzz0pDHEIXYV