A hydraulic oil well pumping system, comprising: an elongated hydraulic cylinder; a piston that is movable between upper and lower rod positions within the cylinder; a rod string that is mechanically connected to and that extends downwardly from the piston, the rod string being configured to extend from a wellhead and into a wellbore for pumping oil from the wellbore; a prime mover; a hydraulic pump that is powered by the prime mover; a directional control valve that moves between upstroke and downstroke flow positions; an oil line fluidly connecting the hydraulic pump and the hydraulic cylinder, the directional control valve being positioned along the oil line so that it can direct flow between the pump and the cylinder; a fluid reservoir for containing hydraulic fluid to be supplied to the pump; a reservoir line that transmits hydraulic fluid from the hydraulic cylinder to the reservoir; an electronic control system that controls movement of the piston as it moves between the upper and lower rod positions by cycling the directional control valve between (i) an "upstroke" condition wherein the hydraulic pump is pumping fluid through the oil line and into the hydraulic cylinder to move the piston to its upper rod position, and (ii) a "neutral" condition wherein the hydraulic pump is no longer pumping fluid into the hydraulic cylinder, but is allowing hydraulic fluid to flow back through the oil line in response to gravitational fall of the piston; and wherein the electronic control system is programmed to determine the location of the piston and to cycle movement of the piston in the hydraulic cylinder based upon volumetric calculations of hydraulic fluid moving into or out of the cylinder, and without reference to position sensors along the wellhead; and further wherein the cycling movement of the piston includes changing an operating speed of the prime mover in response to determining location of the piston. an elongated hydraulic cylinder; a piston that is movable between upper and lower rod positions within the cylinder; a rod string that is mechanically connected to and that extends downwardly from the piston, the rod string being configured to extend from a wellhead and into a wellbore for pumping oil from the wellbore; a prime mover; a hydraulic pump that is powered by the prime mover; a directional control valve that moves between upstroke and downstroke flow positions; an oil line fluidly connecting the hydraulic pump and the hydraulic cylinder, the directional control valve being positioned along the oil line so that it can direct flow between the pump and the cylinder; a fluid reservoir for containing hydraulic fluid to be supplied to the pump; a reservoir line that transmits hydraulic fluid from the hydraulic cylinder to the reservoir; an electronic control system that controls movement of the piston as it moves between the upper and lower rod positions by cycling the directional control valve between (i) an "upstroke" condition wherein the hydraulic pump is pumping fluid through the oil line and into the hydraulic cylinder to move the piston to its upper rod position, and (ii) a "neutral" condition wherein the hydraulic pump is no longer pumping fluid into the hydraulic cylinder, but is allowing hydraulic fluid to flow back through the oil line in response to gravitational fall of the piston; and wherein the electronic control system is programmed to determine the location of the piston and to cycle movement of the piston in the hydraulic cylinder based upon volumetric calculations of hydraulic fluid moving into or out of the cylinder, and without reference to position sensors along the wellhead; and further wherein the cycling movement of the piston includes changing an operating speed of the prime mover in response to determining location of the piston.