Engineering experts probing the Gulf of Mexico oil spill exposed holes in BP's internal investigation as the company was questioned Sunday for the first time in public about its findings.

BP's lead investigator acknowledged that the company's probe had limitations.

Mark Bly, head of safety and operations for BP PLC, told a National Academy of Engineering committee that a lack of physical evidence and interviews with employees from other companies limited BP's study. The internal team only looked at the immediate cause of the April disaster, which killed 11 workers and unleashed 206 million gallons of oil into the Gulf.

"It is clear that you could go further into the analysis," said Bly, who said the investigation was geared to discovering things that BP could address in the short term. "This does not represent a complete penetration into potentially deeper issues."

For example, the National Academy of Engineering panel noted that the study avoided organizational flaws that could have contributed to the blast. BP has focused much of its work on decisions made on the rig, not with the managers on shore.

Najmedin Meshkati, a professor at the Viterbi School of Engineering at the University of Southern California, said he wondered why BP named its report an accident investigation when it left critical elements out. He asked BP to turn over information on shift duration and worker fatigue.