A gas-analysis sample injection system and method for transfer of sample gas from a gas-sample cylinder to an analyzer such as a gas chromatograph, providing a cabinet with a door and a cabinet vent, vent manifold, and vent exhaust, a carrier gas supply, a sample cylinder support bracket, a sample filter housing, and a sample injector valve with an injector-valve actuator. Controlled by a valve controller over valve-control lines, a carrier gas regulating valve and sample-cylinder inflow valve allow carrier gas at regulated pressure into the mounted gas-sample cylinder, and a sample-cylinder outflow valve and sample transfer valve allow flow of sample gas into the sample injector valve. A filter vent valve and injector-valve vent valve operate in coordination with the other valves to provide venting and purging of extraneous gasses.