A gas chromatographic system for the analysis of gas species to be collected from the JET torus and to be processed in the JET active gas handling plant during the active operation phase with deuterium and tritium plasmas was designed and built by CFFTP under contract with JET. The gas‐chromatograph consists of a compression/injection stage and of two parallel, analytical stages, one for the detection of helium, hydrogen, oxygen, nitrogen, methane, carbon monoxide, and the six hydrogen molecules by means of a thermal conductivity detector (TCD) and one for the detection of carbon monoxide, methane, carbon dioxide, and higher hydrocarbons by means of a flame ionization detector (FID). A flow proportional counting detector (FPCD) is placed in series to TCD and FID for the specific analysis of tritiated gas compounds. A detailed description of the system and of its performance will be given which was evaluated using several calibrated gas mixtures including test runs with tritiated species at JET. The gas species mentioned above can be detected in the concentration range from ppm levels to 100%. The estimated error is about 20% at very low concentrations and 1% at high concentrations. The required minimum detection limit for the TCD can be achieved by the injection of large samples and the use of large filament currents. In addition, neon or helium can be chosen as carrier gas. The use of Ne increases the sensitivity for hydrogen and allows the detection of He, whereas He carrier gas gives superior TCD results for all other gases. Due to the high sensitivity of the FPCDs ppb levels of tritiated gas species can be detected.