A pump jack system for reciprocating a pump rod string is made up of a base frame and piston drive cylinders mounted on the base frame with the upper end of the pump rod connected to the cylinder assemblies, the cylinder assemblies being operated in unison by a fluid control circuit communicating with inner and outer concentric fluid passages, and the pump rod string is counterbalanced by a fluid circuit which supplies pressure in an upward direction to each of the pistons on each upstroke and substantially reduces the pressure on each downstroke, the fluid circuit being selected from an inert gas alone or an inert gas pressurizing a hydraulic fluid.