MEXICO CITY/HOUSTON >> An investigation is underway into the fatal chemical leak at a Houston area oil refinery owned by Mexico’s state oil firm Pemex, the company’s top executive said today.

Two contract workers were killed and up to 35 others were treated for exposure to hydrogen sulfide gas during work on a unit at the 312,500-barrel-per-day (bpd) refinery located near Houston.

Pemex, as Petroleos Mexicanos is best known, took full ownership of the Deer Park refinery in early 2021, acquiring Shell’s stake in a refining joint venture. Mexico had acquired the facility to become more self-sufficient in gasoline and diesel.

Pemex Chief Executive Officer Victor Rodriguez told a media briefing that the bodies of two workers were recovered early this morning after the toxic gas had dissipated enough to allow emergency workers to approach the affected area.

“The deceased are not Pemex workers, nor are any of those affected,” said Rodriguez, who noted it remains unclear what caused the chemical release.

The fatalities were externally contracted maintenance workers at the refinery, Rodriguez said. He did not disclose the contractor that employed them.

Work was underway on a sulfur recovery unit at the time, according to people familiar with the matter.

The CEO, who took over earlier this month, said three or four units were shut at the refinery. The company hopes to return to normal operations later today.

In 2021, Shell disclosed the agreement to sell its interest in Deer Park to its former partner Pemex for some $596 million.

Pemex’s domestic refineries have for years suffered a series of accidents, including explosions and fires, that have caused deaths in Mexico.

Additional reporting by Ana Isabel Martinez and Raul Cortes Fernandez.