British energy giant BP says it has temporarily managed to stop oil flowing into the Gulf of Mexico from a leaking well.
It is the first time the oil flow has stopped since an explosion on the Deepwater Horizon rig on April 20.
The well has been sealed with a cap and tests will be carried over the next two days to see whether it is working properly.
President Barack Obama welcomed the development as "a positive sign", but cautioned that BP was still in the testing period.
Even if there are no leaks over the next two days, it will be weeks before BP hopes it will be able to completely shut down the well.
The gulf oil spill is the worst environmental disaster in U.S. history. It has so far cost BP $3.5 billion.
The cleanup is expected to take years.
compiled from agency reports