Tom L. Ward plans to acquire the majority of privately-held Riata Energy Inc., Amarillo, Texas, from the company's founder Malone Mitchell and other shareholders for $500 million. Ward will acquire 29 million shares at $17.25 per share. He expects to retain 23.2 million shares after he transfers 5.8 million to a family limited liability company, and will join Riata as chairman and chief executive. Ward was president, chief operating officer and a director of Oklahoma City-based Chesapeake Energy Corp. Mitchell will retain approximately 22 million shares and continue as president, COO and a director.