Abstract: An unloader apparatus for a gas compressor having a compressor cylinder and a reciprocating compressor piston slidable in the compressor cylinder. The unloader apparatus comprises a hollow sleeve positioned in a suction line of the gas compressor with a port therethrough for communicating gas from the suction line to a suction valve. An unloader piston is slidably disposed within the hollow sleeve and is movable between an open position opening the port whereby gas flow to the suction valve is prevented and a closed position closing the port. In its closed position, the unloader piston seals the compressor cylinder and the compressor piston reciprocates in a partial vacuum. Actuating means connected to the unloader piston is provided for moving the piston between its respective positions. The actuating means utilizes high pressure gas from the discharge side of the compressor for sliding the unloader piston between its positons and exhausts the gas to the suction side of the compressor.