A commission investigating the catastrophic BP oil spill in the Gulf of Mexico began public hearings in New Orleans on Monday with a vow to work "thoroughly, independently and impartially."

U.S. President Barack Obama, centre, with BP oil spill commission co-chairs Bob Graham, left, and William Reilly speak to reporters at the White House on June 1. (Pablo Martinez Monsivais/Associated Press)U.S. President Barack Obama established the commission after the April 20 explosion on the Deepwater Horizon oil rig off the Louisiana coast. The explosion killed 11 workers and blew out the well the rig was drilling, setting off an environmental crisis.

"I wish we had the immediate power to stop the gushing" of oil into the Gulf, commission co-chair and former Florida senator Bob Graham said in his introductory remarks.

"That is beyond our ability," said Graham, who also served eight years as Florida governor. "But we do promise to give our very best efforts to find out what is happening and the enormous consequences of the spill ... on the Gulf region."

"[We will work] thoroughly, independently and impartially," said co-chair William Reilly, a former administrator of the Environmental Protection Agency. "We will follow the facts wherever they lead."

The panel started by focusing on the response to the spill, its economic effects and the deepwater offshore drilling moratorium, which the Obama administration revised to Nov. 30 on Monday, instead of why it happened.

Larry Dickerson, president of Diamond Offshore Drilling Inc., which is the No. 2 deepwater drilling contractor, turned the focus on the first day from the effects of the spill to who's to blame.

Dickerson told the hearing what a hardship the president's drilling moratorium was. But in criticizing what the Obama administration calls a "pause" in drilling, advocates placed the blame on BP.

Dickerson, whose company is down from 10 rigs to seven because of the moratorium, said the stoppage is "a slow-motion domino fall" in his industry.

Senator Mary Landrieu, a Democrat from Louisiana, told commissioners that the moratorium is costing jobs.

"One hundred twenty thousand people could be out of work in Louisiana alone," Landrieu said. "This is a very serious issue."

At the start of the hearing, BP senior vice-president Kent Wells testified about what BP was doing to try to stop the leak. None of the seven commissioners asked him about the causes of the rig explosion, and Wells did not discuss the question of blame.

The bipartisan national commission on the BP spill will receive input from experts and members of the public during two days of hearings in New Orleans, with a view to developing options to prevent and deal with future offshore oil spills.