NEW ORLEANS — Oil giant BP PLC said in an internal report released today before a key piece of evidence has been analyzed that multiple companies and work teams contributed to the massive Gulf of Mexico spill that fouled waters and shorelines for months.

In its 193-page report posted on its website today, the British company described the incident as an accident that arose from a complex and interlinked series of mechanical failures, human judgments, engineering design, operational implementation and team interfaces.

BP spread the blame around, and even was critical of its own workers' conduct, but it defended the design of its well and it was careful in its assessments. It already faces hundreds of lawsuits and billions of dollars of liabilities. In public hearings, it had already tried to shift some of the blame to rig owner Transocean and cement contractor Halliburton. BP was leasing the rig from Transocean and owned the well that blew out.

The report was generated by a BP team led by Mark Bly, BP's head of safety and operations.

BP's report is far from the final word on possible causes of the explosion, as several divisions of the U.S. government, including the Justice Department, Coast Guard and Bureau of Ocean Energy Management, Regulation and Enforcement, are also investigating.