Residents were told to stay inside and close all windows and doors to prevent exposure to the toxic hydrogen sulfide gas.

DEER PARK, Texas (AP) — Two employees killed when hydrogen sulfide leaked at a Houston-area oil refinery were employees of a subcontractor performing maintenance work, the director of Pemex, Mexico's state-owned oil company that operates the plant, said Friday.

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,

A Texas sheriff says two workers at a Houston-area oil refinery were killed after hydrogen sulfide leaked at the plant