HOUSTON — A buckled section of drill pipe caused the malfunction of supposedly fail-safe equipment when a BP well in the Gulf of Mexico blew out last April, killing 11 workers and spewing millions of barrels of oil into the Gulf of Mexico, according to a report released by the Interior Department on Wednesday.

The report, a detailed analysis by a Norwegian company that was hired as part of the federal investigation into the spill, could lead to design changes in blowout preventers, the industry-standard devices that are the last line of protection to prevent drilling disasters. It might also prompt changes in the procedures that rig workers use to control subsea wells.

Federal and industry investigators have long theorized that the force of the blowout deep in BP’s Macondo well mangled a piece of pipe within the blowout preventer, stopping its rams and blades from cutting the pipe and shutting off the flow of oil. But the failure of the blowout preventer was only one in what investigators have said was a series of causes of the disaster, including shortcomings in the well design, a faulty cement job and errors of judgment by drilling managers and crew members.

The report, written after technicians spent months tearing apart and examining the 53-foot-tall blowout preventer at a NASA facility in Michoud, La., did not assign responsibility to BP; Cameron International, which manufactured the preventer; or Transocean, which owned and maintained it along with the Deepwater Horizon rig that was drilling the well.