Firefighting boats had battled the blaze since Saturday aboard the Burgos, which is owned by the company, Petroleos Mexicanos, or Pemex.
A Pemex statement Sunday night said experts have begun investigating to determine what caused the fire in two of the ship's tanks. It said specialists from a Texas salvage company had boarded the vessel.
Pemex said a flight over the ship had determined that only a minimal amount of fuel was in the water and it was contained by floating booms.
Earlier in the day, the company had said the Burgos' double hull had prevented any fuel spill . . .