More than three days since BP started using a new, tighter fitting cap to stop the oil from gushing out of the well 1.6km below the surface, the British energy giant said the cap was holding.

in depth

Earlier on Sunday, BP officials had expressed hope that the test of the cap which began Thursday could continue until a relief well being drilled reaches the damaged well and heavy drilling mud and cement is used to seal it more permanently.

Doug Suttles, BP's chief operating officer, told reporters on Sunday that reopening the well would release oil into the Gulf for up to three days even though capture vessels were standing by on the surface to begin processing oil within hours.

"We're hopeful that if the encouraging signs continue that we'll be able to continue the integrity test all the way to the point that we get the well killed," he told reporters before Allen issued his statement.

"Clearly we don't want to reanimate flow into the Gulf if we don't have to."

Before the cap was placed, nearly 10 million litres of oil was spewing into the Gulf every day for nearly three months since BP's rig exploded and sank in late April, according to the US government's worst case projections.

BP was able to siphon some of that oil to ships on the surface but was not able to shut off the flow until fitting the cap on Thursday.