An untested procedure to plug the blown-out oil well in the Gulf of Mexico seemed to be working, officials said Thursday, but new estimates showed the spill has already surpassed the Exxon Valdez as the worst in U.S. history.
Meanwhile, President Obama moved aggressively to show his of the environmental disaster.
Coast Guard Admiral Thad Allen told WWL Radio in New Orleans that the risky oil-plug procedure known as "top kill" appears to be working "so far" and that no oil is leaking into the Gulf. Crews are currently pumping mud into the well and waiting for pressures in the well to stabilize before attempting to cement the well shut from the top.
Allen says they are "cautiously optimistic" but are not ready yet to declare victory.
If oil stops flowing to the surface in the Gulf of Mexico, BP officials will know that their latest effort to plug a blown-out undersea well off the Louisiana coast was successful.
But new oil flow estimates by scientists studying the blown-out well would make the leak , far bigger than the 11 million gallons that spilled in the Exxon Valdez disaster. U.S. Geological Survey Director Dr. Marcia McNutt said the results are preliminary, but two teams determined the well has spilled between 17 and 39 million gallons.
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At a White House news conference Thursday, Mr. Obama defended his administration's response to the Gulf oil spill, saying they have been singularly focused on the disaster.
The president said that all steps BP takes to end the huge spill must be approved in advance by the government and that his administration will do whatever is needed to protect and restore the Gulf Coast from this "unprecedented disaster."
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After Mr. Obama's press conference, Louisiana Republican Gov. Bobby Jindal told reporters "We don't need our federal government making excuses for BP."
Marine scientists also said Thursday they have discovered a massive new plume of what they believe to be oil deep beneath the Gulf, stretching 22 miles from the leaking wellhead northeast toward Mobile Bay, Ala. The discovery by researchers on the University of South Florida College of Marine Science's Weatherbird II vessel is the second significant undersea plume recorded since the rig exploded.
David Hollander, associate professor of chemical oceanography at the school, says the thick plume was detected just beneath the surface down to about 3,300 feet and is more than 6 miles wide. Scientists are worried the plumes may be from chemicals used to break up the oil.
BP PLC was pumping heavy mud into the leaking well, and executives said Wednesday night that there had been no problems so far. Still, BP Chief Executive Tony Hayward said engineers would not know until at least Thursday afternoon whether the latest remedy was having some success.
If top kill stops the flow, BP would then inject cement into the well to seal it. The top kill has worked above ground but has never before been tried 5,000 feet beneath the sea. BP pegged its chance of success at 60 to 70 percent.
BP managing director Bob Dudley compared the top kill attempt to an "arm wrestling" match between two almost equal competitors; the heavy mud being pumped from above, and the geyser of oil shooting up from beneath the seafloor.
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From a drill ship, a 30,000 horsepower engine - equivalent to 50 Indy 500 cars - began pumping heavy drilling fluid a mile down into the well's broken five-story blowout preventer on Thursday. BP's goal is to overwhelm the gushing oil and gas with superior force - to bully it back down - and then seal it off with cement, reports CBS News correspondent Mark Strassmann.
"Think about sucking coke through a straw," said Dr. Ed Overton, an environmental scientist at Louisiana State University. "They want to switch from coke to a milkshake which slows it down, and ultimately get such a thick milkshake it won't flow at all."
There were concerns, reports Strassmann, that if the pressure of the oil shooting from the well is too great, the top kill attempt could actually force the broken valves open even wider, making the spill worse.
Fishermen, hotel and restaurant owners, politicians and residents along the coast are fed up with BP's failures to stop the oil that is coating Louisiana's marshes and the wildlife that relies on them. The anger has turned toward President Obama and his administration.
The Thursday, as Mr. Obama moved more aggressively to take charge of the oil spill. Elizabeth "Liz" Birnbaum, the head of the U.S. Minerals Management Service, had run the service in the Interior Department since July 2009.
Americans expressed frustration with both the global oil giant and Mr. Obama for their handling of the environmental disaster.
Only 18 percent of those polled said they approved of how BP was acting in response. An overwhelming majority -- 70 percent -- said they disapproved. Mr. Obama fared slightly better, with 45 percent saying they disapproved of his handling of the crisis. That still represents an overall negative rating, however, as only 35 percent said they approved of his words and deeds since the disaster struck.
Sarah Rigaud, owner of Sarah's Restaurant in Grand Isle is tired and nervous. The oil has to be stopped, she said.
"The tourists won't come," Rigaud said Wednesday, serving lunch to a half-full restaurant of mostly oil workers and local politicians who are worrying themselves.
"It makes me very nervous. I have anxiety attacks," she said. "Every day I pray that something happens, that it will be stopped and everybody can get back to normal."
Also Wednesday, the Coast Guard pulled commercial fishing boats from oil cleanup efforts in Breton Sound off the Louisiana coast after several people became ill. Crew members on three vessels reported nausea, dizziness, headaches and chest pains, the Coast Guard said.
CBS affiliate WWLTV reports seven people were hospitalized and were being treated for contact with the chemical dispersant BP is releasing underwater to try and break up the crude before it surfaces.
Taslin Alfonso, a spokesperson for West Jefferson Medical Center, told WWLTV it "seems to be the case" that some of the men have worse conditions than the rest, but the hospital wouldn't release any further information.
Alfonso said the workers do believe that the dispersant caused their symptoms.
The Coast Guard told all 125 commercial vessels that were helping clean up spilled oil to return to shore. Medical workers evaluated the crew members as a precaution.
The gusher began after an offshore drilling rig exploded April 20, killing 11 workers. Dozens of witness statements obtained by The Associated Press show a combination of equipment failure and deference to the chain of command aboard the rig impeded the system that should have stopped the gusher before it became an environmental disaster.
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Additional leaks springing from the top kill solution were a grave risk, said Anil Kulkarni, a mechanical engineering professor at Penn State.
"One scenario is that it may make things worse," Kulkarni said. "If it ruptures all over, then it would be even more difficult to close it."
Suttles said BP had not detected any new leaks as of Wednesday night.
He said within the next day, if oil stops flowing to the surface, then engineers will know the drilling fluid being pumped in was starting to work. Engineers were monitoring the well's pressure readings constantly to determine how much oil was escaping.
If not, the company had several backup plans, including sealing the well's blowout preventer with a smaller cap, which would contain the oil. An earlier attempt to cap the blowout preventer failed. BP could also try a "junk shot" - shooting golf balls and other debris into the blowout preventer to clog it up - during the top kill process.
Last week, the company inserted a mile-long tube to siphon some of the oil into a tanker. The tube sucked up 924,000 gallons of oil, but engineers had to dismantle it during the top kill.
A permanent solution would be to drill a second well to stop the leak, but that was expected to take a couple months.
Some 100 miles of Louisiana coastline had been hit by the oil, the Coast Guard said.
When will they stop the oil and can they? They were questions on the lips of residents in Grand Isle at the bottom tip of Louisiana.
"Certainly there's hope. But the reality for us is that whether they cap it or not, we're still going to have an ecological and economic disaster down here, one that we don't know whether or not we'll be in a position to recover," Jefferson Parish Sheriff Newell Normand said.
In Pass a Loutre, the odor wafting above the oily water was that of an auto shop.
"There's no wildlife in Pass a Loutre. It's all dead," Plaquemines Parish President Billy Nungesser said.
Louisiana-raised Democratic strategist James Carville has been critical of the administration response and hoped Obama's visit Friday would change that.
"I think you're going to see some real action," once the president sees the oiled coast, Carville said.