Patterson-UTI ( PTEN - Get Report) plunged 8% after the oil driller said it believes an unnamed former officer may have embezzled $70 million over more than five years.

The Snyder, Texas, company said its audit committee began an investigation into unauthorized payments for assets that weren't delivered to the company. The panel will hire lawyers and forensic accountants to investigate.

Patterson said it was telling the Securities and Exchange Commission and other authorities.

Its shares fell $2.81 to $30.02.