BP shares rose modestly on Friday after the group confirmed it had temporarily stopped oil flowing into the Gulf of Mexico from its leaking well.
At the close of trading, shares were up 1.3%, having risen as much as 5% earlier in the day.
It is the first time the flow has been stopped since an explosion on the Deepwater Horizon rig on 20 April.
The well has been sealed with a cap as part of a test of its strength that could last up to 48 hours.
BP, however, remains cautious about the success of the latest development.
"The sealing cap system never before has been deployed at these depths or under these conditions, and its efficiency and ability to contain the oil and gas cannot be assured," the company said in a statement.
"Even if no oil is released during the test, this will not be an indication that oil and gas flow from the well bore has been permanently stopped."
US President Barack Obama said the development was a "positive sign" but noted that BP was still in the testing phase.
BP is drilling two relief wells which will relieve pressure under the seabed and hopefully permanently stop the flow of oil.
As of Monday, BP said it had spent $3.5bn (£2.3bn) dealing with the disaster which began with a fire and explosion aboard the Deepwater Horizon drilling platform that killed 11 workers.
