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 w…