White House spokesman Robert Gibbs on Wednesday hailed the 'beginning of the end' of efforts to stop the leak and contain the oil in the Gulf of Mexico. 'It is sort of the beginning of the end of the sealing and containment phase of this operation,' Gibbs told reporters. 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 5 million barrels of oil into the ocean for nearly three months in the world's worst accidental marine spill. Gibbs also said: 'There's a lot of reasons why there's no ' Mission Accomplished' banner.' '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.' 