California Code, Public Resources Code - PRC § 3316.11

“Working interest” means an interest held in lands by virtue of fee title, including lands held in trust, a lease, operating agreement or otherwise, under which the owner of such interest has the right to drill for, develop and produce oil and gas. A working interest shall be deemed vested in the owner thereof even though his right to drill or produce may be delegated to an operator under a drilling and operating agreement, unit agreement, or other type of operating agreement.