WASHINGTON: The chief executive of BP says he is ”personally devastated” by the Gulf of Mexico oil disaster, but that it is too early to decide what caused the mishap or to nominate with certainty when the leak will be plugged.In prepared remarks that were to be delivered overnight to a House of Representatives’ energy and commerce subcommittee in Washington, Tony Hayward said he understood the animosity that Americans feel towards him and his company.The explosion and sinking of the Deepwater Horizon oil rig ”never should have happened and I am deeply sorry that they did”, he said.”My sadness has only grown as the disaster continues.”None of us yet knows why [the accident] happened. But, whatever the cause, we at BP will do what we can to make certain that an incident like this does not happen again.”BP confirmed on Wednesday that it will set aside $US20 billion ($23 billion) over four years to compensate those hit by the disaster, a coup for President Barack Obama, who has been trying to assure Americans he will force the company to pay ”every last dime” of the clean-up.The amount has not been capped, nor have the rights of individuals or states to sue BP, meaning the cost to the oil giant can be expected to escalate.The company is also providing $US100 million immediately for workers affected by a six-month moratorium imposed by the government on new deepwater exploration in the gulf .Mr Obama welcomed the payout. ”What this is about is accountability … At the end of the day, it’s what every American wants and expects,” he said.Mr Hayward’s appearance before the committee is his first since the April 20 explosion that killed 11 workers and sank the Deepwater Horizon. Earlier this week, executives from other oil companies appeared before Congress and sought to distance themselves from BP.But Mr Hayward’s statement, while agreeing that BP was the responsible party in the matter, hinted that others could be drawn into a legal fight.”This is a complex accident, caused by an unprecedented combination of failures. A number of companies are involved, including BP, and it is simply too early to understand the cause.”Mr Hayward was less confident of success in attempts to cap the leak, saying BP could not ”guarantee the outcome of these operations”.”But we are working around the clock with the best experts from government and industry.”Two relief wells being drilled to take over from the crippled well were not expected to be completed before August, but represented ”the ultimate solution to stopping the flow of oil and gas”.BP expects to be able to siphon about 90 per cent of the oil flow into tankers by mid-July, as much as 80,000 barrels a day.However, some observers feared the operation could further weaken the structure of the well, which has been damaged by attempts to staunch the leak.Mr Hayward was sure to face condemnation from the House subcommittee.Responding to his planned testimony, committee member Bart Stupak, a Democrat, said: ”It’s not going to ring true with me or the American public … He’s just going to say, ‘I’m sorry, it’s not going to happen again’. It’s not good enough.”