MEXICO CITY/HOUSTON, Oct 11 (Reuters) - 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 on Friday.

Two contract workers were killed and up to 35 others 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 on

Friday 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 on Friday.

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.