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WASHINGTON (AP) — BP CEO Tony Hayward expects to tell Congress he is "personally devastated" by the Gulf drilling rig explosion and oil spill and understands the anger Americans feel toward him and his company.

The explosion and sinking of the BP-operated Deepwater Horizon rig "never should have happened — and I am deeply sorry that they did," he said in testimony to be delivered to a House panel Thursday. "My sadness has only grown as the disaster continues."

A copy of Hayward's testimony was obtained Wednesday by The Associated Press.

"To be sure, neither I nor the company is perfect," Hayward said. "But we are unwavering in our commitment to fulfill all our responsibilities." He said the British-based company has spent nearly $1.5 billion since the April 20 explosion, and won't stop until the job is done.

Newly disclosed documents obtained by the AP show that after the sinking of the Deepwater Horizon, BP made a worst-case estimate of 60,000 barrels a day flowing into the Gulf of Mexico. That figure is far higher than the company had said publicly until this week, when the government released its own worst-case estimate of about 60,000 barrels a day.

The undated estimate by BP, apparently made sometime last month, reflected the actual situation as it was understood by BP at the time, said Sen. Chuck Grassley, R-Iowa. Grassley, the senior Republican on the Senate Finance Committee, obtained the documents as part of an investigation into the oil spill and its aftermath.

Grassley said it was not clear when exactly BP made the calculation. "Certainly Americans have a right to know that BP made these estimates, the date these estimates were determined and why they were not disclosed at that time," he said.

In a letter to BP America President Lamar McKay, Grassley asked BP to explain when it calculated a worst-case scenario of 60,000 barrels a day and to provide documents justifying the figure.

Hayward will appear before the House Energy and Commerce Committee's oversight and investigations subcommittee, which is investigating the explosion that killed 11 workers and unleashed a flood of oil that has yet to be stemmed. He called it "a complex accident, caused by an unprecedented combination of failures."

Hayward has been a juicy target for lawmakers and other critics — once saying "I'd like my life back." Before that happens, he'll have to survive a hearing that some are describing as a public execution.

"I expect him to be sliced and diced," said Rep. Bart Stupak, D-Mich., chairman of the subcommittee.

Here's advice from a Washington lawyer, Stan Brand, who specializes in criminal law and Congress: "Put on your asbestos suit and get ready."

Thursday will be Hayward's inaugural appearance since the largest oil spill in U.S. history. At earlier hearings, company executives such McKay testified alongside other witnesses.

This week, Hayward flies solo. He might as well show up with a big X on his forehead.

"There's nobody else in front of the firing squad," Brand said. "It's about as far from a legally recognizable proceeding as you're going to see. It will be a much more dramatic public execution" than the earlier congressional hearings.

Another lawmaker, Rep. John Dingell, a Michigan Democrat and former committee chairman, also predicted a rough road for Hayward on Capitol Hill.

"He's going to have, if I'm any judge of the committee and the temperament of the members, a very unpleasant afternoon," Dingell said.

Hayward has said he's got thick enough skin to handle the verbal assaults.

"I'm so far unscathed," he told analysts in a recent conference call, referring to the general criticism he's received. "No one has actually physically harmed me. They've thrown some words at me. But I'm a Brit, so sticks and stones can hurt your bones but words never break them, or whatever the expression is."

Charles Tiefer, a professor of legislative studies at the University of Baltimore Law school and former House general counsel, said witnesses in Hayward's situation often will have practice sessions in front of "murder boards," in which experts in crisis management and public relations throw the most hostile questions they can.

"There's no substitute for getting worked over by your own side for preparing you for a fierce reception," Tiefer said.

The BP CEO follows a long list of corporate faces used as congressional punching bags. Just this year, executives from Goldman Sachs spent nine hours trying to fend off accusations from senators that they bilked investors, and Toyota President Akio Toyoda personally and repeatedly apologized for deadly defects in his company's cars, only to have angry lawmakers forcefully respond that was hardly sufficient.

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Associated Press writers Matt Apuzzo and Eileen Sullivan contributed to this report.