One-half of the cut and cap is done. Now comes the hard part -- putting a lid on the Gulf oil gusher.
BP sliced off the main pipe on the leaking oil well with giant shears Thursday in the latest bid to curtail the worst oil spill in U.S. history, but the cut was jagged, and a looser fitting cap will be needed.
The inverted funnel-like cap slightly wider than the severed pipe will be placed over the spewing oil. A rubber seal on the inside will attempt to keep oil from escaping, though engineers acknowledge some crude will still come out.
"We'll have to see when we get the containment cap on it just how effective it is," said Coast Guard Adm. Thad Allen, the government's point man for the disaster.
BP PLC turned to the giant shears after a diamond-tipped saw became stuck in the pipe halfway through the job, yet another frustrating delay in the six-week-old spill. The cap could be set over the gusher as early as Thursday night.
If the cap can be put on successfully, BP will siphon the oil and gas to a tanker on the surface.
"It's an important milestone, and in some sense, it's just the beginning," BP CEO Tony Hayward said.
This latest attempt is risky because slicing away the section of the 20-inch-wide riser removed a kink in the pipe, and could temporarily increase the flow of oil by as much as 20 percent.
Live video footage showed oil spewing unimpeded from the top of the blowout preventer, but Allen said it was unclear whether the flow had increased.
"I don't think we'll know until the containment cap is seated on there," he said. "We'll have to wait and see."
Crews will also use methanol to try to prevent icylike crystals from forming on the inside of the cap. At this depth a mile underwater, the near-freezing temperatures can cause a buildup up of hydrates, which foiled the company's attempt to place a 100-ton, four-story dome over the leak about a month ago.
The Deepwater Horizon rig, about 50 miles off the coast of Louisiana, exploded on April 20, killing 11 workers. An estimated 500,000 to 1 million gallons of crude has been spewing into the Gulf daily, and the company has failed so far to plug the busted well.
The damage to the environment was chilling on East Grand Terre Island along the Louisiana coast, where workers found birds coated in thick, black goo. Images shot by an Associated Press photographer show Brown pelicans drenched in thick oil, struggling and flailing in the surf.
Anywhere between 21 million and 46 million gallons of oil has spewed into the Gulf, according to government estimates.
BP's Hayward promised Thursday that the company would clean up every drop of oil and "restore the shoreline to its original state."
"BP will be here for a very long time. We realize this is just the beginning," he said.
Associated Press writer Paul J. Weber in Houston contributed to this report.