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Welders in Port Fourchon, Louisiana, scurry on Monday to finish a 93-ton, four-story-tall oil-containment "dome." The giant box is the key component of one of three "subsea oil recovery systems" intended to be lowered onto three seafloor leaks spilling an estimated 210,000 gallons (795,000 liters) of oil a day into the Gulf of Mexico.

(See aerial pictures of the Gulf of Mexico oil spill.)

The leaks resulted from the mysterious sinking of the BP-leased Deepwater Horizon oil rig on April 22. (See "Rig Explosion Shows Risks in Key Oil Frontier.")

The first of the structures is scheduled to ship out Tuesday night and be in place early next week, according to Elizabeth Ashford, a spokesperson for BP. If all goes well, the spewing oil will be trapped in the boxes and piped up to a ship, where it will be processed and ferried ashore.

"It is a way to collect, we expect, about 85 percent of the oil coming out of the main leak site," Ashford said.

—John Roach

Photos: Huge Containment "Domes" for Gulf Oil Spill

Designed to be dropped onto the Gulf of Mexico's seafloor oil leaks, three building-size oil-containment chambers are nearing completion.