BP has changed its tune once again on the precise timing of when it believes it will be able to contain the oil gushing from its blown-out well in the Gulf of Mexico.

BP said on Wednesday it is dialing back a prediction by its chief operating officer that the leaking oil would be reduced to a "relative trickle" by next week. It now says it will take more time to reach that point.

COO Doug Suttles now says BP hopes to have an improved containment system operating by Monday or Tuesday, a far weaker claim than the one he made Tuesday while speaking in Gulf Shores, Ala.

BP sought to clarify Suttles' comments, saying that even though the company is optimistic it can make measurable progress in the next week in reducing the flow, it will take more time to reach the point that the spill amounts to a trickle.

In the meantime, Suttles has continued to insist that no underwater oil plumes have been detected in "large concentrations" from the spill in the Gulf.

Suttles' comments came Wednesday morning on network news shows, a day after the government said water tests confirmed the presence of underwater oil plumes from the spill, but said that concentrations are "very low."

Suttles told NBC's "Today" show that it "may be down to how you define what a plume is here."

NOAA Administrator Jane Lubchenco said Tuesday that the tests conducted at three sites by a University of South Florida research vessel confirmed oil as far as 3,300 feet below the surface 42 miles northeast of the well site.

A cap placed on the ruptured well last week to channel much of the billowing oil to a surface ship collected about 620,000 gallons Monday and another 330,000 from midnight to noon Tuesday, BP said.

That would mean the cap is collecting better than half the escaping oil, based on the government's estimate that around 600,000 to 1.2 million gallons a day are leaking from the bottom of the sea.

BP plans to bring in an oil-burning device and a tanker from the North Sea as it tries to contain the crude spewing into the Gulf.

A team of researchers and government officials and run by the director of the U.S. Geological Survey is studying the flow rate and hopes to present its findings in the coming days on what is already the biggest oil spill in U.S. history.

In an interview with The Associated Press, team member and Purdue University engineering professor Steve Wereley said it was a "reasonable conclusion" but not the team's final one to say that the daily flow rate is, in fact, somewhere between 798,000 gallons and 1.8 million gallons.

Whatever the amount, all that oil has to end up somewhere. The floating production and storage vessel BP plans to bring in could be part of the answer, officials said.

"It's being brought in because it can handle far more oil than this well is producing," said Wine, who did not know where the vessel would come from or when it would arrive.

The burn rig will be moved away from the main leak site so the flames and heat do not endanger other vessels, BP spokesman Max McGahan said.

Depending on which model is used and its settings, it can handle from 10,500 to 630,000 gallons of oil a day, according to promotional materials by Schlumberger Ltd., the company that makes the device and whose website touts it as producing "fallout-free and smokeless combustion."

It's unclear how many times the EverGreen burner has been used, but it has been proposed for at least one offshore rig in the North Sea to get rid of unwanted gases produced during oil processing.

Environmental documents produced as part of that project, an exploration well proposed by Total E&P of Britain, said burning the oil posed "a moderate risk to the environment" that would release sulfur dioxide, nitrous oxides, methane and other chemicals.

But Wilma Subra, a chemist with the Louisiana Environmental Action Network, said BP should avoid burning the captured oil -- which she said raises new health risks -- and instead bring in more processing equipment.

"This is one of those decisions that will have negative impacts," she said. "Even though it's crude dispersed in water, the burning of crude will raise some health issues."

When it sells the oil recovered from the Gulf, BP will use the revenues to create a fund to protect wildlife in the region, the company said.

In the seven weeks since the oil rig explosion that set off the catastrophe, BP has had to improvise at every turn. The most recent government estimates put the total amount of oil lost at 23.7 million to 51.5 million gallons.

When asked why BP did not have containment systems on standby in case of a leak, BP spokesman Robert Wine said there was no reason to think an accident on this scale was likely.

"It's unprecedented," he said. "That's why these caps weren't there before."

The government is keeping an eye on how BP is reimbursing people for their losses in the Gulf. Allen has written to BP CEO Tony Hayward demanding "more detail and openness" about how the company is handling mounting damage claims, reminding the beleaguered executive that his company "is accountable to the American public for the economic loss caused by the oil spill."

Allen has noted that "working claims is not something that's part of BP's organizational competence."

Obama is scheduled to return to the Gulf Coast on Monday and Tuesday for a two-day update on the Gulf oil spill.

The Associated Press contributed to this report.