Engineers pushed forward with efforts to plug a disastrous Gulf of Mexico leak Saturday as locals and officials crossed their fingers that the untested "top kill" process would work.
A day after President Barack Obama visited the region for the second time since the oil spill began in April, energy giant BP could offer little but assurances that the bid was ongoing, but that it was too early to judge its success.
"It's not a nice little black and white operation and they've got to take it as it comes," said Robert Wine, a spokesman for the British firm.
"None of it's a firm deadline because we're not, if you like, working to a clock, we're working to the intimations of the well."
Wine said crews were continuing to pump heaving drilling fluid called "mud" into the leak, and had also tried a "junk shot," where various type of debris are placed into the leak site to try to clog it up.
But he reiterated that BP would not know if the bid was working until at least Sunday afternoon.
In an attempt to bring new urgency to the effort, Obama toured some of the spill-affected areas in Louisiana on Friday and pledged "to continue to do whatever it takes to help Americans whose livelihoods have been upended by the spill."
Clad in hiking boots, Obama said he would triple the number of workers clearing up soiled beaches, after he saw the effects of the spill up close, picking up and examining tar balls that washed ashore in Louisiana.
"I'm here to tell you that you're not alone. You will not be abandoned. You will not be left behind," he promised to local residents. "We are on your side and we will see this through."
Since the oil spill began, after an April 20 explosion tore through the Deepwater Horizon rig killing 11 workers, an estimated 12,000 to 19,000 barrels of crude a day have been gushing into the Gulf.
BP has sought to assure locals and the government it is doing all it can to stop the spill, but the depth of the leak -- some 5,000 feet below surface -- and the environmental damage already apparent has left many angry at the firm.
On Friday, Admiral Thad Allen, the former Coast Guard commandant charged with overseeing the spill response said intial signs suggested the "top kill" was working.
"They have been able to push the hydrocarbons down with the mud. The real challenge is to put enough into the well to keep the pressure where they can put a cement plug over the top," he said on ABC's "Good Morning America."
But the New York Times said Saturday that the bid was marked by "an apparent lack of progress," and suggested that official might soon move to their next available option -- a containment dome that could capture the leaking oil.
The disaster has already closed stretches of coastal fishing waters, endangering livelihoods which are also dependent on tourism, and threatening a catastrophe for Louisiana marshes, home to many rare species.
Government data released Thursday suggested between 18.6 million gallons and 29.5 million gallons of oil have poured into the Gulf -- far more than the roughly 11 million gallons of crude spilled in the 1989 Exxon Valdez disaster.
Amid the environmental catastrophe, there were also growing fears for the health of cleanup workers exposed to the oil and chemical dispersants.
Four more crewmen aboard ships helping burn off surface oil were evacuated to hospital late Friday after falling ill, a day after the US Coast Guard announced that seven workers were evacuated for medical emergencies.
Obama said 910,000 meters (three million feet) of hard boom had already been deployed in an effort to stop the oil spill reaching wetlands and beaches. But he admitted "there's a limited amount" available.
"We're going to try to get more boom manufactured, but that may take some time," he said.
The commander of a federal research ship who has spent five days out at sea on the edges of the slick said a heavy smell of oil hung over the area.
"It's a strong smell out there," said commander Shepard Smith of the Thomas Jefferson, a 204-foot survey vessel. "It smells like freshly creosoted railroad ties."
BP said Friday the oil spill had cost the firm about 930 million dollars, while the company's market value has also dropped by billions.
Explore further: Oil from Russian trawler wreck reaches Canaries' beaches