(Bloomberg) – BP Plc lowered nearly to the seafloor a 40-foot-tall structure that may capture as much as 85 percent of the oil leaking from a well into the Gulf of Mexico.

The containment system hasn’t begun working yet and the exact timeline for installing the containment box remains “fluid,” said Mark Salt, a spokesman for BP in Houston. If it works properly, it would capture crude from the largest leak at a well that began spilling oil after the Deepwater Horizon rig exploded and sank in the Gulf last month.

“It’s gone a long way down, but it’s not ready yet,” he said. “They’re prepping the seabed, making sure everything is safe down there.”

The box, a rectangular structure with a pyramid-dome on top, is designed to send oil from the Macondo well and channel it through pipes to a tanker in the Gulf where it will be stored and taken to shore. BP, based in London, owns the well, which is about 5,000 feet (1,524 meters) below the water’s surface. The rig was owned by Geneva-based Transocean Ltd.

Similar boxes have been used to funnel crude from leaking wells in shallow water before. This is the deepest deployment of the system, according to a fact sheet provided by BP.

The water depth adds uncertainty to the effort and it may take a week to determine if the system is working, Robert Dudley, BP’s executive vice president for the Americas and Asia, said in Boston yesterday.

There are 10 robots on the sea floor at the site, Dudley said yesterday.

Before the box can be deployed, robots must make sure the area is clear, Salt said. The seabed currently has jagged pipes from the rig, which sank two days after an April 20 explosion, he said.

BP fell 13.1 pence, or 2.3 percent, to 553.9 pence at 4:35 p.m. in London. The shares have dropped 15 percent since the rig exploded.

To contact the reporter on this story: Jessica Resnick-Ault in New York at jresnickault@bloomberg.net

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