BP is using undersea robots in a bid to jam a tube into a broken pipe that is gushing oil into the Gulf of Mexico.
The attempt to divert the oil flow came as workers readied a so-called “top hat” containment dome to be lowered over the leak.
Some scientists have significantly raised their estimate of the rate of oil flow, as the surface slick has grown to 3,650 sq miles (9,500 sq km).
Several US senators have proposed a ban on drilling off the Pacific coast.
Five thousand feet (1,500m) below the surface on Friday, remote-controlled robots were attempting to thread a six-inch (15cm) tube surrounded by a stopper into the 21-inch pipe spewing crude oil and natural gas at a high rate into the water.
If the attempt is successful, the tube could siphon leaking oil and gas into a tanker on the surface, allowing oil workers to concentrate on cleaning up the already-spilled crude.
In addition, BP was preparing to deploy a metal box, or top hat, to cap the leak. A previous attempt to lower a bigger box on to the well site failed.
