Abstract: A downhole hydraulically operated pump having a power piston reciprocated by alternating pressurized hydraulic fluid flow controlled at the surface by a hydraulic power control system which quickly reverses the flow direction. The pump housing, suspended in the well fluid of a cased well by a discharge tube, has a power piston chamber in which the power piston is housed, a production piston chamber in which a production piston is housed, and an intermediate fluid and gas collection chamber disposed therebetween. The power piston, production piston, and a suction filter are connected by an elongate hollow tubular piston rod to reciprocate together and the piston rod interior is in communication with the discharge tube. On up strokes, a series of check valves direct well fluid upwardly through the suction filter, the piston rod interior, the production piston, the production piston chamber, the piston rod interior, and into the discharge tube.