WILLISTON (AP) - Federal officials are investigating the death of a man who fell at an oil rig site in eastern Montana.

Clinton Mosby, 20, of Williston, died Feb. 16. He was at a rig site about 40 miles west of Sidney, said Richland County (Mont.) Coroner Marvin Johnson.

A preliminary investigation indicated steps leading from a tank battery up to a rig floor gave way, and that Mosby fell at least 8 feet. Other workers tried to revive him but he was pronounced dead at the Sidney Health Center.

Federal Labor Department spokesman Rich Kulczewski said the Occupational Safety and Health Administration investigation began last week.

"OSHA has up to six months to complete the investigation," Kulczewski said. "We don't rush it. We'll look at what the root cause was, what the conditions of the site were and what the safety precautions were."