NEW ORLEANS - Hundreds of thousands of gallons of oil are being allowed to spew into the fouled waters of the Gulf of Mexico while BP engineers prepare to install a new containment system they hope will catch it all in the coming days.
There's no guarantee for such a delicate operation nearly a mile below the water's surface, officials said, and the permanent fix of plugging the well from the bottom remains slated for mid-August.
"It's not just going to be, you put the cap on, it's done. It's not like putting a cap on a tube of toothpaste," Coast Guard spokesman Capt. James McPherson said.
Robotic submarines removed the cap that had been placed on top of the leak in early June to collect the oil and send it to surface ships for collection or burning. BP aims to have the new, tighter cap in place as early as Monday and said that, as of Sunday morning, the work was going according to plan. BP hopes the capping operation will be done within three to six days.
Kent Wells, a BP senior vice president, said during a Sunday morning news briefing he was pleased with the progress but cautioned that unforeseen bumps could lie ahead.
"We've tried to work out as many of the bugs as we can. The challenge will come with something unexpected," Wells said.
If tests show the new cap can withstand the pressure of the oil and is working, the Gulf region could get its most significant piece of good news since the April 20 explosion on the BP-leased Deepwater Horizon rig, which killed 11 workers.
It would be only a temporary solution to the catastrophe. Hope for permanently plugging the leak lies with two relief wells, the first of which should be finished by mid-August.
With the cap removed Saturday at 12:37 p.m. CDT, oil flowed freely into the water, collected only by the Q4000 surface vessel, with a capacity of about 378,000 gallons. That vessel should be joined Sunday by the Helix Producer, which has more than double the Q4000's capacity.
But the lag could be long enough for as much as 5 million gallons to gush into already fouled waters. Officials said a fleet of large skimmers was scraping oil from the surface above the well site.
The process begun Saturday has two major phases: removing equipment currently on top of the leak and installing new gear designed to fully contain the flow of oil.
BP on Sunday said it had successfully removed the top flange that had only partially completed the seal with the old cap, almost a day earlier than a previous estimate.
Now that the top flange is removed, BP is considering whether it needs to bind together two sections of drill pipe that are in the gushing well head. The following step involves lowering a 12-foot-long piece of equipment called a flange transition spool onto the well head and bolting it to the bottom flange still in place.
After the spool is bolted in place, the new cap - called a capping stack or "Top Hat 10" - can be mounted. The equipment, weighing some 150,000 pounds, is designed to fully seal the leak and provide connections for new vessels on the surface to collect oil. The cap has valves that can restrict the flow of oil and shut it in, if it can withstand the enormous pressure.
That will be one of the key items for officials to monitor, said Paul Bommer, a professor of petroleum engineering at the University of Texas at Austin.
"If the new cap does work and they shut the well in, it is possible that part of the well could rupture if the pressure inside builds to an unacceptable value," Bommer wrote in an e-mail Saturday.
Ultimately, BP wants to have four vessels collecting oil within two or three weeks of the new cap's installation. If the new cap doesn't work, BP is ready to place a backup similar to the old one on top of the leak.
The government estimates 1.5 million to 2.5 million gallons of oil a day are spewing from the well, and the previous cap collected about 1 million gallons of that. With the new cap and the new containment vessel, the system will be capable of capturing 2.5 million to 3.4 million gallons - essentially all the leaking oil, officials said.
The plan, which was accelerated to take advantage of a stretch of good weather forecast to last seven to 10 days, didn't inspire confidence in residents of the oil-slicked coast.
"I want to believe it and I'm going to take them at their word because it's good news," Mayor Tony Kennon of Orange Beach, Ala., said Saturday.
But for the popular tourist destination, any halt to the leak comes too late to save the season, Kennon said.
Louisiana State University environmental sciences professor Ed Overton said he's less concerned with the strategy than with the unknown. As long as the cap is put on properly, the plan should work, he said.
"The problem is that almost everything they've done, there's been some unknown about it," he said. "I don't see why this is all that much different."
Associated Press Writers Vicki Smith in New Orleans and Carrie Schumaker in Washington contributed to this report.