Abstract: A mandrel valve and gas lift valve mechanism that is adapted to be interconnected in a production tubing string within a well in order to produce fluid from the well under conventional gas lift methods. A plurality of gas lift valve mechanisms, which may be referred to as mandrel assemblies, may be dispersed or spaced in accordance with any suitable gas lift system design or, if desired, may be connected in end-to-end relationship defining a cluster of gas lift valves at each of several levels within the well. Each of the mandrel assemblies may include a gas lift valve and a mandrel valve that function to produce fluid only when the mandrel valve is open. Certain ones of the mandrel valves may be maintained in the open condition thereof while others of the valves may remain selectively closed during production operation.