BP pins its hopes on giant box to halt Gulf oil spill

The quest took on added urgency as oil reached several barrier islands off the Louisiana coast, many of them fragile animal habitats. Several birds were spotted diving into the oily, pinkish-brown water, and dead jellyfish were washed up on the uninhabited islands.

The oil was extending westward to fishing areas around the Mississippi Delta.

Once the containing box reaches the sea floor, underwater robots will secure it over the main leak, a process that will take hours.

If the delicate procedure works, the device could be collecting as much as 85 per cent of the oil spewing into the Gulf and funnelling it up to a tanker by tomorrow.

But it has never been tried so far below the surface, where the water pressure is enough to crush a submarine.

"We haven't done this before," said BP spokesman David Nicholas. "It's very complex and we can't guarantee it."

The company is in charge of cleaning up the mess in the Gulf. It was leasing the drilling rig Deepwater Horizon when it exploded 50 miles offshore on April 20, killing 11 workers and blowing open the well. An estimated 200,000 gallons a day have been flooding out in the nation's biggest oil spill since the Exxon Valdez disaster in Alaska in 1989.

The technology has been used a few times in shallow waters, but never at such extreme depths. The box must be accurately positioned over the well, or it could damage the leaking pipe and make the problem worse.

Other risks include ice clogs in the pipes – a problem that crews will try to prevent by continuously pumping in warm water and methanol – and the danger of an explosion when separating the mix of oil, gas and water that is brought to the surface.

"I'm worried about every part, as you can imagine," said David Clarkson, BP vice president of engineering projects.

If the box works, a second one now being built may be used to deal with a second, smaller leak from the sea floor.

Meanwhile, the huge oil slick remains floating in the Gulf, and residents of Louisiana, Mississippi, Alabama and Florida are anxiously waiting to learn when it might come ashore.

Damage to marine life already done

Despite the latest efforts to contain the oil leak, experts warn that damage to marine wildlife has already been done.

Small globs of oil the consistency of tar or asphalt will roll around the sea's bottom, trapped hundreds of feet below the surface and will move with the current.

Scientists warn that bacteria, plankton and other tiny, bottom-feeding creatures will consume oil, and will then be eaten by small fish, crabs and shrimp meaning the damage will be passed up through the food chain.