OKLAHOMA CITY (AP) — Oklahoma City-based Chesapeake Energy Corp. says four top executives have left the company as part of an ongoing reorganization effort.

Chesapeake CEO Doug Lawler announced the moves Monday in emails obtained by The Journal Record and The Oklahoman.

Lawler says chief operating officer and executive vice president Steve Dixon; executive vice president Jeff Fisher; senior vice president Steve Miller; and senior vice president Martha Burger "are leaving the company to pursue other opportunities."

Lawler told The Oklahoman that the changes are part of an ongoing effort to reduce expenses and improve performance.

"On behalf of the entire company, I want to express our gratitude to Steve, Jeff, Steve and Martha for their many years of service and dedication," Lawler wrote. "Each of these executive leaders has contributed greatly to Chesapeake, and we wish them the very best in their future endeavors.

"I have great confidence in the operations, drilling, and HR teams," he said in the email. "I will continue to be directly engaged in each of these important areas, and I have appointed interim management responsibility as we move forward with our operational strategy shift."

Chesapeake co-founder and former CEO Aubrey McClendon left the company in April while senior vice presidents Tom Price and Henry Hood left the company in May.