Abstract: A pump jack having a walking beam oscillated in a vertical arc by a hydraulic actuating cylinder that receives pressurized hydraulic fluid from a variable displacement pump. The hydraulic actuating cylinder is controlled by a hydraulic valve having an operating member mechanically shifted by a second hydraulic actuating cylinder near the end points of the pivotation arc of the walking beam to reverse the direction of movement of the walking beam during the shifting of the operating member of the hydraulic valve. The second hydraulic actuating cylinder is controlled by a second hydraulic valve that transmits pressure to the second hydraulic actuating cylinder from the variable displacement pump and reverses the flow of pressurized hydraulic fluid to the ports of the second hydraulic actuating cylinder near the end points of the pivotation arc of the walking beam.