BILLINGS, Mont. (AP) — Representatives of Exxon Mobil Corp. are denying that the company acted negligently in the case of a worker who died while checking an oil storage tank in eastern Montana.

The Texas-based company on Thursday filed its response to a recent lawsuit from the estate of 30-year-old Trent Vigus of Glendive. Vigus died in July 2010 while working for an Exxon contractor, Nabors Industries.

An attorney for his estate said Vigus' common-law wife began to suspect negligence years after the accident, when reading about another worker who died while working on an oil storage tank.

Plaintiff's attorney Fred Bremseth says the case is similar to others where workers were overcome by dangerous fumes from storage tanks and died.

Exxon spokeswoman Suann Guthrie says an autopsy determined Vigus died of natural causes.