A House panel looking into what may have caused the oil rig explosion in the Gulf of Mexico revealed Wednesday that a key piece of equipment intended to prevent such incidents had significant problems.

Rep. Bart Stupak, chairman of the Energy and Commerce Subcommittee on Oversight and Investigations on Wednesday outlined issues with the blowout preventer that may have prevented it from engaging.

“Our investigation is at its early stages, but already we have uncovered at least four significant problems with the blowout preventer used on the Deepwater Horizon drill rig,” the Michigan Democrat said at the hearing in which executives from BP and three other companies involved with the oil exploration project testified.

Stupak said the blowout preventer, which is intended to stop the flow of oil from the rig, had a significant leak in a hydraulic system, had been modified in unexpected ways, did not have sufficient power to cut through a drill pipe and had a dead battery that may have caused a switch not to operate.

Lamar McKay, the president of BP America, has testified that the blowout preventer was supposed to be the fail-safe mechanism that would prevent the type of explosion that occurred. The blowout preventer is part of the rig that is owned by Transocean and is manufactured by another company, Cameron.

Officials from BP, Transocean, Cameron and Halliburton, which cemented the well, also testified before the House panel on Wednesday. It was the second day that energy company executives faced grilling by lawmakers on Capitol Hill about the deadly incident that has prompted calls by lawmakers and the White House for changes in oil drilling regulation.

Stupak also said his committee had uncovered a document prepared by Transocean in 2001, when it bought the blowout preventer from Cameron, which said there were 260 “failure modes” that could require the piece of equipment to be pulled.

“How can a device that has 260 failure modes be considered fail-safe?” Stupak asked.

In his testimony Jack Moore, president of Cameron, stated that Cameron invented the blowout preventer in the 1920s and that it has had a long history of reliable performance. He said it was too early to draw conclusions about how the incident occurred.

Rep. Henry Waxman, chairman of the Energy and Commerce Committee, criticized BP and its partners, saying the explosion was caused by equipment and operational failures.

Waxman, a California Democrat, said that James Dupree, BP’s senior vice president for the Gulf of Mexico, told committee staff that a pressure test on the well on April 20, the day of the explosion, came up with results that were “not satisfactory” and “inconclusive.” Dupree told the committee staff that another test was conducted which was also unsatisfactory that could have shown that an influx of gas was causing pressure to mount inside the wellbore.

Dupree told the committee staff that he believed the well blew moments after the second pressure test. But Waxman said that lawyers for BP contacted the committee staff on Tuesday and said that further investigation revealed that more pressure tests were taken which led company officials to end testing and proceed with well operations.

Waxman said that information reviewed by his committee also shows debate between Transocean and BP officials about how to proceed.