BP PLC reported that mud forced down the well overnight was pushing the crude back down to its source for the first time since the Deepwater Horizon rig exploded off Louisiana on April 20, killing 11 workers.

The effort is progressing, giving officials high confidence that no more oil will leak into the Gulf, retired Coast Guard Adm. Thad Allen, the government's point man on the spill response, said at a news briefing in Washington. But he stressed the containment effort isn't over.

Crews that performed the so-called "static kill" overnight now must decide whether they should follow up by pumping cement down the broken wellhead. Officials won't declare complete victory until they get into the well from the other end, and that won't happen until later this month.

"This job will not be complete until we finish the relief well and pump mud and cement in through the bottom," Allen said.

The upbeat news coincided with the release of a federal report Wednesday indicating that only about a quarter of the spilled oil remains in the Gulf and is degrading quickly, with the rest contained, cleaned up or otherwise gone.

The remaining oil, much of it below the surface, remains a threat to sea life and Gulf Coast marshes, said Jane Lubchenco, administrator of the National Oceanic and Atmospheric Administration. But the spill no longer poses a threat to the Florida Keys or the East Coast, according to the report by NOAA and the Interior Department.

President Barack Obama, while noting that people's lives "have been turned upside down," declared that the operation was "finally close to coming to an end."

A Florida State University oceanographer who has long been tracking the spill, and who early on challenged the government's low estimates of its size, called the report "spin."

"There's some science here, but mostly it's spin, and it breaks my heart to see them do it," said the oceanographer, Ian MacDonald. "This is an unfortunate report. I'm afraid this continues a track record of doubtful information distributed through NOAA."

The calculations were based on daily operational reports, estimates by scientists and analyses by experts. The government acknowledged it made certain assumptions about how oil dissolves in water naturally over time.

Lubchenco defended the report, saying authors used direct measurements and the best estimates available and have a high degree of confidence in them. The numbers can be updated as new information comes in, she noted.

Nearly three-quarters of the oil — more than 152 million gallons — has been collected at the well by a temporary containment cap, been cleaned up or chemically dispersed, or naturally deteriorated, evaporated or dissolved, the report said.

That leaves nearly 53 million gallons in the Gulf. The amount remaining — or washed up on the shore — is still nearly five times the size of the 11 million-gallon Exxon Valdez spill, which wreaked environmental havoc in Alaska in 1989.

About a quarter of the oil evaporated or dissolved in the warm Gulf waters, the same way sugar dissolves in water, federal officials said. Another one-sixth naturally dispersed because of the way it leaked from the well. Another one-sixth was burned, skimmed or dispersed using controversial chemicals.

Nearly 207 million gallons leaked from the well in total, according to government estimates. The cap held back nearly 35 million gallons.

Charter boat captain Randy Boggs, of Orange Beach, Ala., said Wednesday he has a hard time believing BP's claims of success with the static kill and similarly dismissed the idea that only a quarter of the oil remains in the Gulf.

"There are still boats out there every day working, finding turtles with oil on them and seeing grass lines with oil in it," said Boggs, 45. "Certainly all the oil isn't accounted for. There are millions of pounds of tar balls and oil on the bottom."

At the entrance to Gulf Islands National Seashore at Pensacola Beach, Fla., Don Allen still wasn't expecting to sell many snow cones or Italian sausages from his food truck.

"I don't know where it went if it's not out there," said Allen, who had to lay off his son because business has been so slow as tourists abandoned beaches over the summer. "It's all just numbers, and it has changed so often."

BP applied nearly 2 million gallons of a chemical dispersant to the oil as it spewed from the well, an attempt to break it into droplets so huge slicks wouldn't tarnish shorelines and coat marine animals, and to encourage it to degrade more quickly.

Lawmakers in Washington pressed scientists Wednesday to explain what effects the chemical will have on the Gulf's ecosystem.

Sen. Sheldon Whitehouse, D-R.I., called use of the chemicals a "grand experiment" that didn't guarantee limited damage from the spill or make clear whether greater harm was possible.

The 75-ton cap placed on the well in July had been keeping the oil bottled up inside over the past three weeks but was considered only a temporary measure. BP and the Coast Guard wanted to plug up the hole with a column of heavy drilling mud and cement to seal it off more securely.

BP chief executive Tony Hayward is stepping down in October amid criticism of his handling of the spill and cleanup efforts. White House spokesman Robert Gibbs said Wednesday that no one owes him an apology despite the new confidence that cleanup efforts are working.

He said results would have been different if federal officials had not pushed BP "at every step of the way" for a quicker, more thorough response.