The White House on Wednesday hailed the "beginning of the end" of efforts to stop the leak and contain the oil spill in the Gulf of Mexico.

"It is sort of the beginning of the end of the sealing and containment phase of this operation," White House spokesman Robert Gibbs told reporters at a daily press briefing.

He made the remarks after BP succeeded overnight in plugging its runaway well by ramming in heavy drilling mud for eight hours which drove the oil back down into the reservoir miles beneath the seabed.

BP's Macondo well ruptured after an oil rig exploded and sank on April 20, spewing up to 4.9 million of barrels of oil into the ocean for nearly three months in the world's worst accidental marine spill.

"There's a lot of reasons why there's no 'Mission Accomplished' banner," Gibbs said.

"There's a lot of work to do," he said. "We're not leaving the area, and more importantly, we're not leaving behind any commitment to clean up the damage that's been done and repair and restore the Gulf."

Meanwhile, U.S. President Barack Obama said Wednesday that the long battle against the huge Gulf of Mexico oil spill is close to an end.

"The long battle to stop the leak and contain the oil is finally close to coming to an end," Obama said at the start of a speech to the American Federation of Labor and Congress of Industrial Organization in Washington.

In addition to stopping the gusher, most of the oil that leaked into the Gulf has been captured or dispersed, Obama said.

U.S. National Incident Commander Thad Allen also said Wednesday that oil company BP's effort to plug the leak was progressing, giving officials "high confidence" that there will soon be no more oil leaking into the environment.

The upbeat assessment came as a government report released Wednesday said about 74 percent of the oil that leaked from BP's damaged well in the Gulf of Mexico is gone from the Gulf or has degraded into tiny particles.

"It is estimated that burning, skimming and direct recovery from the wellhead removed one quarter (25 percent) of the oil released from the wellhead," said the report, titled "BP Deepwater Horizon Oil Budget: What Happened to the Oil?"

Another 25 percent naturally evaporated or dissolved and 24 percent was dispersed, either naturally or "as the result of operations," into small droplets, the report said.

The report was produced by a team led by the Interior Department and National Oceanic and Atmospheric Administration.

The remaining 26 percent of oil is either on or just below the surface as light sheen and weathered tar balls, washed ashore or buried in sand and sediment, according to the report.