The hearings came as MMS announced that one of its top offshore drilling officials, Chris Oynes, is resigning. The agency has often been accused of leniency in its regulations, and Oynes' resignation came on the heels of President Barack Obama's promise to halt a "cozy relationship" between the agency and the industry.
An MMS spokesman said Oynes' retirement, after 34 years in the government, had to do with his wife's retirement plans -- and nothing to do with the deadly oil rig explosion that led to the spill in the gulf.
"Is he being forced out? The answer is absolutely not," spokesman Drew Malcomb told AOL News.
MMS did not respond to a request to testify before the Senate's homeland security committee, drawing a rebuke from Sen. Susan Collins, R-Maine, and its chairman, Sen. Joseph Lieberman, I-Conn.
Lieberman vowed to "haul the Minerals Management Service before our committee at some time in the not-too-distant future" if the agency doesn't answer its questions.
BP America President Lamar McKay told the committee that his company's engineers are collecting roughly 20 percent of the oil and gas leaking from a pipe at the bottom of the gulf, using a mile-long pipe connected to a tube that is siphoning the oil to a tanker on the surface.
Lieberman said he put much of the blame for the disaster on MMS for not forcing companies like BP to figure out how to cap a leaking oil well in the darkness and immense pressure of a mile below the water's surface.
"I wish that [BP] had done more to prepare for this, but I must say ... I hold the Minerals Management Service responsible" for failing to plan for such a large-scale disaster, Lieberman said.
The Senate panel's probe is one of several under way into the explosion and fire aboard the Deepwater Horizon rig on April 20 that killed 11 workers and led to the sinking of the rig and the oil leak that poses a growing environmental threat. Some scientists fear the leak is five to 10 times larger than the official estimate of 200,000 gallons per day.
Doug Suttles, BP's chief operating officer, said the company is trying to adjust the undersea tube mechanism so that more than 20 percent can be captured. He said the device is capable of containing up to half of the leak.
Suttles said success at containing some of the leak will be followed with an attempt at plugging the pipe altogether.
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"We're very encouraged by this, but this doesn't stop the flow -- it just attempts to capture it," Suttles said at a news conference in Robert, La.
Suttles said efforts could begin late this week at a "top kill" operation, which would force heavy mudlike matter downward into the well to stop the upward flow of oil and gas. If successful, the mud would be followed with cement, which could stop the flow altogether.
BP is drilling two relief wells, intended to allow engineers to cement the well shut 18,000 feet below the water's surface. Success with the relief well would mark the end of the well's production, Suttles said.
"The right thing to do is permanently plug this well, and that's what we will do," Suttles said.
McKay testified that it could be August before a relief well can plug the well permanently.
Mike Williams, one of the last crew members to escape the rig, told CBS's "60 Minutes" that the crew was told it would take 21 days to drill down to the oil, but it took six weeks. Williams, the chief electronics technician, said a BP manager ordered the crew to pick up the pace.
Williams said: "And he requested to the driller, 'Hey, let's bump it up. Let's bump it up.' And what he was talking about there is he's bumping up the rate of penetration. How fast the drill bit is going down."
The faster pace caused the bottom of the well to split open, which led to the well being abandoned. A new well had to be drilled, which cost BP more than two weeks and millions of dollars, the "60 Minutes" report said.
"We were informed of this during one of the safety meetings, that somewhere in the neighborhood of $25 million was lost. ... And you always kind of knew that in the back of your mind when they start throwing these big numbers around that there was going to be a push coming. A push to pick up production and pick up the pace," Williams said.
When asked if the crew was pressured after this, Williams said: "There's always pressure, but yes, the pressure was increased."
Suttles said he had not watched the program.
Coast Guard Rear Adm. Mary Landry said forecasts call for calm seas, meaning crews would resume burning heavy concentrations of oil on the surface. Skimming boats would resume trying to collect oil, and air crews were spraying chemical dispersants onto the slick, she said.
Scientists said they've also found vast plumes of oil in the gulf, extending deep below the gulf's surface. Raymond Highsmith of the National Institute for Undersea Science and Technology said he has done preliminary testing and found masses of oil lingering under the surface.
However, a top federal scientist today disputed news media reports of the plumes as "misleading, premature and, in some cases, inaccurate."
"Characterization of these layers will require analysis of samples and calibration of key instruments. The hypothesis that the layers consist of oil remains to be verified," Jane Lubchenco, chief of the National Oceanic and Atmospheric Administration, said in a written statement.