Allen said in statement he had met with U.S. Energy Secretary Steven Chu, U.S. Geological Survey Director Marcia McNutt and other scientists and geologists, officials from BP and other industry representatives to review how the testing of the well cap a mile below the surface of the Gulf of Mexico will be done.
"As a result of these discussions, we decided that the process may benefit from additional analysis that will be performed tonight and tomorrow," Allen said Tuesday.
He said two collection systems, the Helix Producer and the Q4000, are on line and skimmers were being sent to the site in anticipation of any increased oil flow during the transition.
Allen said two relief wells being drilled nearby had reached depths of 17,840 feet and 15,963 feet below the surface.
The testing, once it starts, could take up to 48 hours and involves closing the cap, "effectively shutting in the well," BP said in a release.
Doug Suttles, BP's chief operating officer for exploration and production, said if the tests show the pressure rising and holding, with no significant damage to the casing pipe, BP, working with government scientists, could decide to leave the valves closed, effectively shutting off the well, The New York Times reported Tuesday.
"The best-case scenario is that pressures rise to the point we anticipate they would," Suttles said during a briefing Monday. "We'd likely be able to keep the well shut in."
If tests show pressure lower than expected, that could mean the well is leaking elsewhere into surrounding rock, Suttles said. If that happens, keeping the cap closed could damage the well further.
Suttles said engineers and scientists would evaluate risks based on the pressure results, and various collection systems would be on standby if it were decided to leave the well shut.
Crews added the Helix Producer to the oil collection system Monday, The (New Orleans) Times-Picayune reported. The vessel has the capacity to collect as much as 25,000 barrels of oil per day.
Oil has been gushing since the Transocean Deepwater Horizon rig leased by BP exploded April 20 and sank two days later about 50 miles off the Louisiana coast, killing 11 people.
At the daily White House press briefing, Press Secretary Robert Gibbs said the administration is "hopeful" the approach will work.
"And we are soon to be at a containment capacity that I think will allow people to feel that there isn't oil actively leaking into the gulf, and that will be a big moment," he said.
Gibbs said the response has "a long, long way to go in cleaning up what's in the water and restoring the health and the beauty of the gulf to what it was not just 85 or 86 days ago, but the way it should be. And that's going to take months to develop that plan and years to fix."