Chevron confirmed a fire started at a unit of its Richmond, Calif., refinery. All employees were accounted for, with one minor injury reported.
"We will not speculate on the cause of this incident," the company said in a statement.
Trisha Asuncion, a hazardous materials specialist in the region, said air monitoring detected no hazardous compounds but surveillance would continue, the San Francisco Chronicle reports.
Winds Monday evening pushed most of the smoke from the fire over the region's bay.
The Richmond refinery is the third-largest in California. It can process more than 242,000 barrels of oil per day.
Residents were advised to stay indoors after the blaze erupted. Chevron said that the fire was contained by late Monday. No announcement was made on the effects of the fire or on an expected restart date.