WASHINGTON - U.S. lawmakers channeled Americans' anger and pilloried the boss of the British oil company that caused the massive oil spill in the Gulf of Mexico in a withering day of judgment Thursday.

BP chief Tony Hayward spent the daylong congressional hearing in what appeared to be an attempt to distance himself from day-to-day company policies or decisions that led to the well blowout and America's worst environmental tragedy.

"I'm not stonewalling. I simply was not involved in the decision-making process," Hayward said. That infuriated members of Congress even more, Democrats and Republicans alike.

The verbal onslaught had been anticipated for days and unfolded at a nearly relentless pace.

But with multiple investigations continuing and primary efforts in the Gulf focused on stopping the leak, there was little chance Americans would learn much from Hayward's appearance about what caused the disaster. Yet even modest expectations were not met as the CEO told lawmakers at every turn that he was not tuned in to operations at the well.

Testifying as oil still surged into the Gulf of Mexico and coated ever more coastal land and marshes, Hayward declared "I am so devastated with this accident," "deeply sorry" and "so distraught."

Yet the oil man disclaimed knowledge of any of the myriad problems on and under the Deepwater Horizon rig before the deadly explosion, telling a congressional hearing he had only heard about the well earlier in April, the month of the accident, when the BP drilling team told him it had found oil.

"With respect, sir, we drill hundreds of wells a year around the world," Hayward told Republican Rep. Michael Burgess.

"Yes, I know," Burgess shot back. "That's what scaring me right now."

Republican Rep. Phil Gingrey told the CEO: "I think you're copping out. You're the captain of the ship." Democrats were similarly, if more predictably, livid.

"BP blew it," said Democratic Rep. Bart Stupak, chairman of the House of Representatives investigations panel that held the hearing. "You cut corners to save money and time."

The verbal onslaught had been anticipated for days and unfolded at a nearly relentless pace.

Hayward said his underlings made the decisions and federal regulators were responsible for vetting them. He spoke slowly and calmly in his clipped British accent as he sought to deflect accusations -- based on internal BP documents obtained by congressional investigators -- that BP chose a particular well design that was riskier but cheaper by at least $7 million.

Burgess slammed both the CEO and the government regulators for a risky drilling plan that he said never should have been brought forward.

In a jarring departure that caught fellow Republicans by surprise, Rep. Joe Barton, top Republican member of the panel, used his opening statement to apologize -- twice -- for the pressure put on the company by President Barack Obama to contribute to a compensation fund for people in the afflicted Gulf of Mexico states.

Barton said the U.S. has "a due process system" to assess such damages, and he decried the $20 billion fund that BP agreed to Wednesday at the White House as a "shakedown" and "slush fund." He told Hayward, "I'm not speaking for anybody else. But I apologize."

He later retracted his apologies to BP, then apologized anew -- this time for calling the fund a "shakedown."

Barton's earlier remarks were clearly an embarrassment for the party. BP itself has acknowledged that responsibility for the economic damages lies with them and has offered an initial pledge of $20 billion dollars for that purpose."

Since 1990, oil and gas industry political action committees and employees have given more than $1.4 million to Barton's campaigns, the most of any House member during that period, according to the nonpartisan Center for Responsive Politics.

As Hayward began to testify, a protester disrupted the hearing and was forcibly removed from the room by Capitol police. The woman was identified as Diane Wilson, 61, a shrimper from Texas, near the Gulf Coast. Her hands stained black, she shouted to Hayward from the back of the room: "You need to be charged with a crime."

Stupak, the subcommittee chairman and a former Michigan state trooper, noted that over the past five years, 26 people have died and 700 have been injured in BP accidents -- including the Gulf spill, a pipeline spill in Alaska and a refinery explosion in Texas.

Hayward argued that safety had always been his top priority and "that is why I am so devastated with this accident." When he became CEO in 2007, Hayward said he would focus "like a laser" on safety, a phrase he repeated on Thursday.

Republican Rep. John Sullivan questioned BP's commitment to safety.

BP had 760 safety violations in the past five years and paid $373 million in fines, Sullivan said. By contrast, Sunoco and ConocoPhillips each had eight safety violations and ExxonMobil just one, Sullivan said.

An estimated 278 million to 476 million litres of oil has come out of the breached wellhead, whether into the water or captured.

The reservoir that feeds the well still holds about 7.5 billion litres of oil, according to the first public estimate Hayward has given of the size of the undersea oil field.

That means the reservoir is believed to still hold 94 per cent to 97 per cent of its oil. At the current flow rate, it would take from two years to nearly four years for all the oil to be drained from it.