WASHINGTON (AP) - BP's lead investigator into the Gulf of Mexico oil spill has told an independent panel of experts that the company's internal probe has limitations.

Mark Bly, head of safety and operations for BP PLC, says a lack of physical evidence and interviews with employees from other companies limited BP's study.

Bly is appearing before a National Academy of Engineering committee on Sunday. The April disaster killed 11 people and released 172 million gallons of oil.

BP's study said eight separate failures led to the oil rig accident. The report said BP and other companies were mainly responsible.

But the conclusions were made without examining the drilling rig or a key piece of equipment, the blowout preventer.