Tensions between oil giant BP and oil rig owner Transocean over which company is responsible for the oil spill in the Gulf of Mexico are expected to flare up Tuesday when two Senate panels hold hearings on the deadly incident.

In prepared testimony before the Senate Energy and Natural Resources Committee, a top BP executive and the president of Transocean clashed over whether a piece of the machinery called the blowout preventer failed to prevent the well rupture, which led to the spill.

In his opening statement made public by the committee Monday, Lamar McKay, president of BP North America, pointed to the blowout preventer as an essential “fail-safe” mechanism that closes valves when pressure causes fluid such as oil and gas to enter the well and threatens the rig.

“Transocean’s blowout preventer failed to operate,” McKay stated in his written testimony. “All of us urgently want to understand how this vital piece of equipment and its built-in redundancy systems failed and what measures are required to prevent this from happening again.”

But in his own written testimony, Transocean CEO Steven Newman sharply rebutted the suggestion that the blowout preventer was the major culprit.

“That simply makes no sense,” Newman said. He said the blowout preventer is used during the drilling operation. But at the time of the explosion, he noted, the well had already been drilled and sealed with cement.

He said that well barriers and the cementing and casing of the well were responsible for controlling pressure from the reservoir. Halliburton was the contractor in charge of cementing.

“Certainly we need to understand what happened to the [blowout preventers] and whether changes need to be made to improve the effectiveness of these devices in the unusual circumstances of an accident like the one on April 20,” Newman stated in the written testimony. “But the BOPs were clearly not the root cause of the explosion.”

In the testimony, Newman also noted that BP was the general operator for the oil exploration project, responsible for submitting plans to the government and securing federal permits.

“Once those plans are approved and permits are issued and work begins, the Operator — or leaseholder — serves as the general contractor that manages all of the work that is performed on the lease,” Newman wrote. He added that the general contractor then hires subcontractors, which in this case included Transocean, to assume specific tasks.

While BP’s McKay said the oil giant was committed to investigating what happened, he made clear in his testimony that his company was not the only one involved in the explosion on the Deepwater Horizon rig that resulted in the oil spill.

“Only seven of the 126 on board the Deepwater Horizon were BP employees, so we have only some of the story,” McKay wrote in his testimony. “We are looking at our own actions and those of our contractors.”

McKay also sought to respond to critics who say the spill should prompt the administration and Congress to curb future offshore drilling.

“Tragic and unforeseen as this accident was, we must not lose sight of why BP and other energy companies are operating in the offshore, including the Gulf of Mexico,” he said in the testimony. “The Gulf is one of the world’s great energy producing basins providing one in four barrels of oil produced in the United States. That is a resource that powers America and the world every day, one our economy requires.”