United States authorities say BP has finally sealed the oil well in the Gulf of Mexico that exploded five months ago, causing the worst oil spill in American history.
The official in charge of the spill, Coast Guard Adm Thad Allen, says the well has been successfully capped by a permanent cement plug.
A temporary cap had sealed the flow on 15 July while a relief well was dug. That well finally linked up with the ruptured well on Thursday, allowing workers to start pumping in the cement, removing the need for the cap. A pressure test showed the cement plug was holding.
In a statement, President Barack Obama hailed Sunday's "important milestone" and vowed to continue to help those affected.
He said he remained "committed to doing everything possible to make sure the Gulf Coast recovers fully from this disaster".
The worst offshore oil spill in US history began after the Deepwater Horizon rig blew up on 20 April, killing 11 workers and later sinking.
The disaster has brought an environmental nightmare to hundreds of miles of US coast. It led to BP chief executive Tony Hayward standing down and the imposition of a moratorium on deepwater offshore drilling.
The cost of the disaster to BP has been massive. It has created a compensation fund of $US20 billion and paid out another $US8 billion so far in the clean-up campaign.