The announcement Thursday came after company officials said all valves had been shut on a new cap over the busted well in an experiment to stop the spill.
It was a long-awaited milestone in one of the nation's worst environmental disasters.
While not a permanent solution to plug the busted well, the success in capturing the oil spewing out was welcome news.
The crisis began when BP's deepwater rig exploded, killing 11 workers.
The cap is not a permanent fix. BP is drilling two relief wells so it can pump mud and cement into the leaking well in hopes of plugging it for good.