Three workers are missing after the huge blaze on an oil platform in the Gulf of Mexico that killed four workers and burned for hours.
Petroleos Mexicanos, or Pemex, said it became aware of the missing workers when it recounted personnel after Wednesday's fire on the Abkatun-A Permanente shallow-water platform in the Campeche Sound.
One of the missing workers was from Pemex and the other two were employed by contractor Cotemar, the company said.
Investigators were still trying to determine the cause of the blaze, which injured 16 people, two seriously, and forced the evacuation of 300 workers.
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Pemex said it managed to avert any significant oil spill. Officials said environmental damage was avoided because the fire happened on a processing platform where the feeder lines could be turned off, rather than at an active oil well with a virtually unlimited amount of fuel flowing up from the seabed.
Pemex director-general Emilio Lozoya said the accident "would have a minimal impact on production, because this was a processing platform, not a producing well".
On Wednesday, helicopters flew workers with bandaged hands and faces and burn marks on their overalls to the nearby city of Ciudad del Carmen, where crowds of relatives of oil workers thronged outside hospitals.
Survivors said the blaze engulfed the platform, forcing people to leap into the sea or flee in boats.
Pemex said eight firefighting vessels fought the flames, which shot into the air with thick, billowing smoke. The company said it had managed to transport about 300 workers from the oil rig, the Abkatun Permanente.
Pemex suffered two serious fires and oil spills in the Gulf of Mexico in recent years, including one in 2007 that killed 21 workers. A Pemex gas pipeline explosion killed 26 near the border with the United States in 2012, and in 2013 at least 33 people were killed in a blast at the Pemex headquarters, which was ruled an accident.
The incident considered the worst for Pemex was a 1984 explosion and fire at a gas plant on the outskirts of Mexico City. At least 500 people were believed killed.