A BP executive says the company has stopped oil leaking from its ruptured Gulf of Mexico well for the first time since April.
Senior BP vice-president Kent Wells said the oil flow stopped as the last of three valves on a huge capping stack was shut about 2.25pm on Thursday.
Workers are now conducting a critical pressure test, which could take from six to 48 hours.
The test will show whether the cap can safely shut off the flow from the well if oil-capture vessels at the surface must disconnect.
Officials stress the move does not mean the cap will be used to permanently seal the well.
It is the first time the flow of oil has stopped since an explosion on the Deepwater Horizon rig on 20 April that killed 11 workers.
Experts have estimated about 35,000 to 60,000 barrels a day have been flowing into the Gulf for about 13 weeks.