a compressor of the reciprocating piston and cylinder type especially adapted for use in moving gas from the wellhead or casing of a producing oil or gas well into the gas sales line with the compressor being operated by the conventional pump jack utilized to operate a downhole pump and more particularly the walking beam of the pump jack is used as the prime mover for operating the compressor . the compressor includes a long stroke piston reciprocal in a cylinder with the cylinder being attached to the walking beam and the piston rod supported from the pump jack skid or samson post with the attachment structures being unique to enable optimum operating conditions in each installation . the cylinder and piston are constructed of non - metallic components or coated to resist corrosion by various corrosive materials normally found in natural gas . the compressor may be a single acting arrangement in which the compression stroke occurs as the pump rods and downhole pump are descending in the well to use the force of gravity during the compression stroke to enable operation with less expenditure of mechanical energy . the compressor may also be double acting for larger volume capacity and is installed within the actual movement capabilities of the walking beam with adjustable mounting enabling maximum output of the compressor .