METAIRIE, La. -- BP sliced off a pipe with giant shears Thursday in the latest bid to curtail the worst oil spill in U.S. history, but the cut was jagged and placing a cap over the gusher will now be more challenging.
BP turned to the shears after a diamond-tipped saw became stuck in the pipe halfway through the job, yet another frustrating delay in the six-week-old Gulf of Mexico spill.
The cap will be lowered and sealed over the leak, said Coast Guard Adm. Thad Allen, the government's point man for the disaster. It won't be known how much oil BP can siphon to a tanker on the surface until the cap is fitted, but the irregular cut means it won't fit as snugly as officials hoped.
''We'll have to see when we get the containment cap on it just how effective it is,'' Allen said. ''It will be a test and adapt phase as we move ahead, but it's a significant step forward.''
Even if it works, BP engineers expect oil to continue leaking into the ocean.
The next chance to stop the flow won't come until two relief wells meant to plug the reservoir for good are finished in August.
BP Chief Executive Tony Hayward promised the company would clean up every drop of oil, and ''restore the shoreline to its original state.''
''We will be here for a very long time. We realize this is just the beginning,'' Hayward said Thursday.
This latest attempt to control the spill, the so-called cut-and-cap method, is considered risky because slicing away a 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.
Hayward conceded the attempt was risky, but said the risk was reduced when the pipe was cut away.
Live video footage showed oil spewing uninterrupted out of 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.''
President Barack Obama will return to the Louisiana coast Friday to assess the latest efforts, his third trip to the region since the April 20 disaster. It's also his second visit in a week.
The White House said the federal government was sending BP a $69 million bill for costs so far in the spill. Spokesman Robert Gibbs said the bill was the first to be sent to the oil company, which leased the rig that exploded April 20 and sank two days later. Eleven people were killed.
So far, anywhere between 21 million and 46 million gallons of oil has spewed into the Gulf, according to government estimates.
Computer models show oil could wind up on the East Coast by early July, and even get carried on currents across the Atlantic Ocean, by Bermuda and toward Europe.