BP says it's increasingly confident that a new cap on its leaking well in the Gulf of Mexico can be used to block the flow of oil completely, until the leak is permanently sealed.
The flow of oil was stopped on Thursday for the first time, at 2.25pm local time (1925 GMT). The BBC reports testing has continued since then.
Chief operating officer Doug Suttles says BP is hopeful the well can eventually be shut down.
The leak began after a fatal explosion and fire on the Deepwater Explorer on 20 April. The rig sank two days later.
BP has put the costs of dealing with the disaster at over $US3.5 billion. It has already paid more than $US200 million to 32,000 claimants.