The fire that crippled the Carnival Cruise ship triumph apparently started with a leak in a fuel-oil return line.
The US coast guard released its preliminary findings today.
Authorities say the fuel-oil return line was connected to one of the ship's generators, leaking oil hit a hot surface, starting the fire.
More than 4,000 passengers and crew were stranded off the coast of Mexico for five days last week.
The triumph was eventually towed into port in Mobile, Alabama late Thursday night.
The lead investigator praised the ship's crew for doing a "very good job" containing the fire.
The US Coast Guard says the investigation will last several months.