Abstract: Production liquid from a well is pumped to the surface by a hydraulically driven reciprocating piston pump. The pump is driven in a drive stroke by a flow of hydraulic fluid supplied through a single tubing line applied to a drive side of a drive piston and in a return stroke by the weight of the production liquid heavier than the hydraulic fluid applied to the return side of the drive piston. The production liquid is pumped though the well casing. A control valve causes application of pressure in the hydraulic fluid for the drive stroke and release for the return stroke. The pump body includes a first duct communicating between the tubing and the bottom drive side of the drive piston and a second duct communicating between the well casing and the top drive return of the drive piston.