Washington (CNN) -- Executives from BP, Transocean and Halliburton are back in the hot seat Wednesday as a House Energy and Commerce subcommittee questions them about the Gulf Coast oil spill.
The three companies have primarily blamed each other for the accident in April that left 11 workers dead and oil still spewing into the Gulf.
BP, the well's owner and lead operator of the project, has sought to turn attention to Transocean, which had a contract to drill the well for BP using its Deepwater Horizon drill rig.
"Transocean, as owner and operator of the Deepwater Horizon drilling rig, had responsibility for the safety of drilling operations," Lamar McKay, chairman and president of BP America, told the Senate Energy and Natural Resources Committee on Tuesday.
In particular, McKay drew attention to the valve that was supposed to shut off the well in case of an accident. The valve, known as a blowout preventer (BOP), is owned by Transocean.
"Clearly, the BOP remains a critical piece of equipment throughout all operations to ensure well control," he said.
In written testimony before the hearing, Transocean said the blowout preventer performed fine in tests just a week before the accident.
While it's still unclear why the blowout preventer did not work, Transocean chief executive Steven Newman said the preventer is not the ultimate cause of the accident. He says that there must have been a failure of the well's cementing or the casing that holds the wells in place.
Either way, Transocean said it's the responsibility of the well's owner to set all specifications for the drilling process.
"All offshore oil and gas production projects begin and end with the operator ... in this case, BP," Newman said.
Newman took a slightly more conciliatory tone during his testimony, but still sought to shift the focus away from the blowout preventer and to the well itself.
"Here was a sudden, catastrophic failure of the cement, the casing, or both," he said. "Without a failure of one of those elements, the explosion could not have occurred."
The well's cementing was done by Halliburton. But Halliburton's chief safety and environmental officer, Tim Probert, said responsibility lay with either Transocean or BP.
"The casing shoe was cemented some 20 hours prior to the tragic incident," said Probert. "Had the BOP functioned as expected, this catastrophe may well not have occurred."
During the cementing of the well, Halliburton simply followed BP's instructions, he said.
Senators were not impressed with the blame game.
"Shifting the blame does not get us very far," said Republican Sen. John Barrasso of Wyoming. "And it does not change America's need for energy."
Several senators focused on the blowout preventer, and why it didn't work.
"Should we go forward with deep-water drilling when we know these blow out preventers may not function?" asked Democratic Sen. Mary Landrieu, of Louisiana, whose state has been severely affected by the spill.
Elmer Danenberger, former head of the Minerals Management Service, the federal agency that regulates offshore drilling, said the blowout preventers usually work.
But in some cases, such as thick sections where two joints come together, the preventers won't cut through the pipe, which is necessary to pinch it shut and stop leaks.
Senators wanted to know why there weren't more shears on the blowout preventer in case one shear hit a thick spot on the pipe. They also asked why other backup systems were not in place.
"That was going to be in place, but apparently it never happened," Danenberger answered.
It has been speculated that additional shears might make the devices too heavy for older drill rigs to carry.
Minerals Management Service has come under fire as the story of the spill has unfolded. The agency has to balance competing priorities: slowing drilling to ensure safety while also generating royalties for the U.S. government.
On Tuesday, the Obama administration announced plans to split the agency in two to avoid conflicting interests.
MMS has also been accused of being too close to the oil industry, especially after news broke last year that some of its members were partying with and receiving gifts from oil executives.
"You've all seen the records of the sex parties, the pot parties," Democratic Sen. Bill Nelson of Florida told a Senate Environment and Public Works panel in the afternoon. "MMS clearly needs to get cleaned up."
Under federal law, BP, as the lead project operator, is responsible for all clean-up costs associated with the spill. On Monday, BP said it has spent $350 million so far.
But damages caused by closure of fishing grounds, shipping lanes and tourist spots could exceed the cleanup costs, and it's unclear which party will pay those or how much they'll add up to.
Under current law, BP may only be liable for the first $75 million of claims that are expected to run into the billions.
BP has said it will pay all "legitimate claims" when it comes to compensating people for economic loss.
At Tuesday's hearing, BP's McKay said the company expects to spend more than $75 million on compensating people for the spill.
But under questioning from Democratic Sen. Maria Cantwell of Washington, the extent of the commitment wasn't clear.
"So you'll pay for lost fishing opportunities?" asked Cantwell.
"All legitimate claims," responded McKay.
"And lost tourism revenue?" asked the senator.
"All legitimate claims," McKay answered again.
"And how about lost tax revenues to towns and parishes?" asked Cantwell.
"Question mark," said McKay.
"And damages sustained to Louisiana's brand?"
"I really don't know," said McKay.
While the subcontractors are thought to have some legal indemnification from BP and the federal government, lawyers say they could still be open to lawsuits from fisherman and others affected by the spill.
Ultimately, experts have said total costs could range from $2 billion to $14 billion or higher, depending on when the leaking well is closed and where the oil washes ashore.