US Coast Guard Adm. Thad Allen, who is heading the day-to-day federal response to the blowout, Friday morning called the seating of the containment cap "a positive development," but he cautioned that "it will be some time before we can confirm that this method will work and to what extent it will mitigate the release of oil into the environment."
The new cap that undersea robots placed on the leaking pipe appears to be capturing some of the oil, which is rising through a pipe to a ship waiting on the surface.
BP officials say they are encouraged by the results so far.
"But we have only 12 hours' experience with this; we have never done this at 5,000 feet [below sea level] before," cautions Kent Wells, the company's senior vice president for exploration and production. Over the next few days, the BP team will slowly increase the amount of gas and oil flowing up the pipe to a ship receiving the oil. The go-slow approach is designed to avoid a sudden buildup of pressure that might blow the containment cap off the end of the pipe and to keep seawater out of the system.
But it's not expected to capture all of the oil. BP will use dispersants on oil that leaks from the cap – leaking anticipated because the company encountered problems trying to make a clean cut to the top of the pipe spewing the oil.
Hopes of actually stopping the flow now rest with two relief wells BP is drilling. The aim is to use them as conduits for cement, which BP will pump into the leaking well to seal it. The company has said it will take another two months to finish drilling the wells.