Patterson-UTI says three workers missing in Oklahoma oil fire are employees

The Houston-based contract driller said in a statement the cause of the well explosion remains unclear. In total, five workers remained missing late on Monday after the morning blast. None have been identified by local authorities.

"Well control experts and emergency responders are on site and we will conduct a thorough investigation when the incident is fully contained," said chief executive Andy Hendricks in a statement.

"We've reached out to their families and are providing support during this difficult time," he said.

Officials said one of the 22 workers at the site at the time of the explosion was treated for injuries and 16 others were uninjured.

(Reporting by Bryan Sims; Editing by Sandra Maler)