The oil has permeated more than 70 (110km) miles of Louisiana’s coastline
Oil giant BP says it is unsure whether its latest attempt to plug a gushing oil well in the Gulf of Mexico has succeeded.
Chief operating officer Doug Suttles said the "top kill" operation had not yet stopped the flow and it was preparing its next plan.
Millions of gallons of oil have leaked since a rig exploded and sank last month, killing 11 employees.
US President Barack Obama has ordered a tripling of manpower in coastal areas.
The oil spill has been called the worst in US history.
The thick crude has already permeated more than 70 miles (110km) of Louisiana's coastline, threatening fragile wetlands and putting the vital fishing industry at risk.
The "top kill" operation involves pumping shredded golf balls and tyres, as well as thick mud, into the well in an attempt to plug it. It has been going on since Wednesday at a depth of 5,000ft (1.5km).
Mr Suttles said in Louisiana after monitoring the flow: "I don't think the amount of oil coming out has changed. Just by watching it, we don't believe it's changed."
BP had earlier said it would not know for sure if the "top kill" operation had worked until Sunday.
President Barack Obama: “It’s an assault on the shores and our people”
But on Saturday he said he did not know if the operation would succeed, and added that the next option was already being prepared.
This operation is called the lower-marine-riser-package cap.
It involves an underwater robot using a saw to hack off the leaking pipe and place a cap over it.
Mr Suttles said: "If we have to go to it, we can do it as quickly as possible."
Two experts who spoke to Associated Press news agency, Prof Bob Bea, of the University of California at Berkeley, and Eric Smith of the Tulane Energy Institute, both said the results of the "top kill" did not look promising.
The BBC's Andy Gallacher, at Grand Isle beach in Louisiana, says people are growing increasingly impatient and increasingly angry.
He says that for miles in either direction there are small, sticky tar balls and as the waves break against the sand, there is a definite rainbow sheen.
Some fishermen have nailed up signs, our correspondent says, with one reading "BP, you ruined our futures and our heritage".
On Friday, President Obama toured oil-hit areas, saying the US would "do whatever it takes" to help those affected.
He said the additional manpower would lay more booms, clean beaches and monitor stricken wildlife.
A total of 20,000 people have already been deployed to contain and clean up the spill.
Mr Obama said he would take responsibility for "solving this crisis", though he said BP would be held financially accountable for the "enormous damage".
"I'm the president and the buck stops with me," he said.
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