US officials have finally declared BP's broken well in the Gulf of Mexico "dead", five months after a deadly oil rig explosion set off one of the costliest and largest environmental disasters ever.
Although the troublesome well may have been killed once and for all, BP still faces a long uphill battle to clean up the Gulf, a litany of lawsuits, billions of dollars in fines and shareholders angered by the firm's instability after its share price more than halved.
Retired admiral Thad Allen, the US pointman for the government's response to the disaster, said the operation to intersect and cement the deepwater well had been successfully completed.
"With this development, which has been confirmed by the Department of the Interior's Bureau of Ocean Energy Management, we can finally announce that the Macondo 252 well is effectively dead," Allen said.
"Additional regulatory steps will be undertaken but we can now state, definitively, that the Macondo well poses no continuing threat to the Gulf of Mexico."
The announcement marked an anti-climactic end to a five-month battle to cap a busted undersea well that gushed nearly five million barrels (210 million gallons) of oil into the Gulf, the largest maritime spill in history.
No oil has leaked into the Gulf in the three months since the well off the Louisiana coast was plugged in a so-called "top kill" operation, but the US administration insisted that it also be sealed from the bottom with a relief well.
A final pressure test of the cement seal was completed at 5:54 am (1054 GMT), officials said.
"Today, we achieved an important milestone in our response to the BP oil spill -- the final termination of the damaged well that sat deep under the Gulf of Mexico," President Barack Obama said in a statement.
Obama said there was now a diminished need for the massive response to the spill, but "we also remain committed to doing everything possible to make sure the Gulf Coast recovers fully from this disaster."
He vowed to "see our communities, our businesses and our fragile ecosystems through this difficult time."
BP pledged to continue "remedying the harm that the spill caused to the Gulf of Mexico, the Gulf Coast environment and to the livelihoods of the people across the region."
The disaster was triggered by an explosion on the Deepwater Horizon rig -- leased by BP and operated by Transocean Energy -- that killed 11 workers on April 20.
The accident broke pipelines between the rig and the ocean floor, spewing massive amounts of oil into Gulf waters, exposing the oil- and wildlife-rich region's vulnerability to deep sea drilling.
For weeks, every effort to plug the well 5,000 feet (1,500 meters) below the surface of the sea fell short as the spreading oil fouled hundreds of miles of shoreline, closed fishing grounds and threatened fragile ecosystems.
The Obama administration also imposed a moratorium on deepwater drilling, setting back another mainstay of the Gulf economy while the cause of the disaster was under investigation.
Eighty-seven days into the crisis, BP finally succeeded in placing a giant cap over the well that stopped the flow of oil.
But the costs were huge, with local livelihoods disrupted and nearly 70 billion dollars wiped off BP's market value.
BP, whose chief executive Tony Hayward was forced to resign, has spent eight billion dollars trying to contain the disaster and has forecast it will eventually cost the energy giant more than 32.2 billion dollars.
"Although the well is now dead, we remain committed to continue aggressive efforts to clean up any additional oil we may see going forward," Allen said.
Multiple investigations into the disaster are still under way and official responsibility has yet to determined. An internal BP investigation laid some of the blame on its contractors.
BP America's CEO Lamar McKay sought to put a positive spin on the lessons his company has learned from the disaster, saying they would be shared to prevent a repeat in the future.
"We also believe that the industry will gain important insights on how to be better prepared to respond to any future incidents," he said.
Explore further: Obama vows US 'will do more' to battle climate change