BP says it has temporarily stopped oil flowing into the Gulf of Mexico from its leaking well.
It is the first time the flow has 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 integrity that could last up to 48 hours.
US President Barack Obama said the development was a "positive sign" but noted that BP was still in the testing phase.
BP executive Kent Wells said the oil had been stopped at 1425 local time (1925 GMT) and he was "excited" by the progress.
"It is very good to see no oil go into the Gulf of Mexico," said Mr Wells.
BP shares rose in New York trading on Thursday after the flow was stopped, having already performed well over the day.
But BP is stressing that even if no oil escapes for 48 hours, that will not mean the flow of oil and gas has been stopped permanently.
BP chief operating officer Doug Suttles emphasised that there was no reason for "celebration" yet, particularly for those in areas already damaged by oil.
"The job is not finished," he said.
The pressure testing is necessary to check the strength of the well. If the pressure within the cap on top is low, that could indicate oil is leaking out further down the well.
If the pressure remains high, BP and the government will have to decide whether to try to keep the well shut or to leave it open and pipe oil to four vessels on the surface.
The US government's incident commander, Adm Thad Allen, said even if it was successful, the well would be reopened and oil capture by ships on the surface would restart while a seismic test was done.
"We can go back then and put the system under pressure again. Once we are convinced we can certainly consider shutting in the well, that is always possible and we would certainly look to do that."
But he emphasised that the option of shutting in the well - closing all the valves and stopping the flow - was a "side benefit" of the new capping stack.
The priority had always been to increase the amount of oil being captured and piped to the surface, he said.
Whatever happens will be a temporary solution, ahead of a relief well being used permanently to kill the original well with mud and cement. The pressure test will provide useful information for that operation.
Work on both of the relief wells is currently suspended because of the integrity test. One of the relief wells is within 4-5ft horizontally and 100ft vertically of intersecting.
The pressure test was twice delayed before starting on Thursday, once while additional checks were put in place to allay fears it could make the leak worse, and on Wednesday by a leaking piece of equipment.
Meanwhile, BP continues to face political pressure in the US.
A Congressional committee has agreed measures that would ban the firm from new offshore drilling for seven years.
BBC News - BP says oil has stopped leaking from Gulf well
BP official Kent Wells confirmed at a press conference just over an hour ago that oil stopped gushing out of the broken pipe at 2:25pm central time today. Below is a screenshot from the submarine monitoring the oil leak, as you can see there is nothing coming out of the pipe right now:
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It is the first time the flow has 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 integrity that could last up to 48 hours.
US President Barack Obama said the development was a "positive sign" but noted that BP was still in the testing phase.
BP executive Kent Wells said the oil had been stopped at 1425 local time (1925 GMT) and he was "excited" by the progress.
"It is very good to see no oil go into the Gulf of Mexico," said Mr Wells.
BP shares rose in New York trading on Thursday after the flow was stopped, having already performed well over the day.
But BP is stressing that even if no oil escapes for 48 hours, that will not mean the flow of oil and gas has been stopped permanently.
BP chief operating officer Doug Suttles emphasised that there was no reason for "celebration" yet, particularly for those in areas already damaged by oil.
"The job is not finished," he said.
The pressure testing is necessary to check the strength of the well. If the pressure within the cap on top is low, that could indicate oil is leaking out further down the well.
If the pressure remains high, BP and the government will have to decide whether to try to keep the well shut or to leave it open and pipe oil to four vessels on the surface.
The US government's incident commander, Adm Thad Allen, said even if it was successful, the well would be reopened and oil capture by ships on the surface would restart while a seismic test was done.
"We can go back then and put the system under pressure again. Once we are convinced we can certainly consider shutting in the well, that is always possible and we would certainly look to do that."
But he emphasised that the option of shutting in the well - closing all the valves and stopping the flow - was a "side benefit" of the new capping stack.
The priority had always been to increase the amount of oil being captured and piped to the surface, he said.
Whatever happens will be a temporary solution, ahead of a relief well being used permanently to kill the original well with mud and cement. The pressure test will provide useful information for that operation.
Work on both of the relief wells is currently suspended because of the integrity test. One of the relief wells is within 4-5ft horizontally and 100ft vertically of intersecting.
The pressure test was twice delayed before starting on Thursday, once while additional checks were put in place to allay fears it could make the leak worse, and on Wednesday by a leaking piece of equipment.
Meanwhile, BP continues to face political pressure in the US.
A Congressional committee has agreed measures that would ban the firm from new offshore drilling for seven years.
BBC News - BP says oil has stopped leaking from Gulf well
BP official Kent Wells confirmed at a press conference just over an hour ago that oil stopped gushing out of the broken pipe at 2:25pm central time today. Below is a screenshot from the submarine monitoring the oil leak, as you can see there is nothing coming out of the pipe right now:
Link Removed due to 404 Error
