An automated gas chromatographic (GC) system has been developed for the measurement of carbon dioxide, methane, and nitrous oxide in air and other gases. Carbon dioxide is measured by a flame ionization detector (FID) after conversion to methane in pure hydrogen carrier gas, using palladium and nickel dual catalysts which permit direct on-line injection of oxygen-containing samples. The detector measures methane in the same sample, although the system has not been optimized for this gas. Nitrous oxide is measured in a separate aliquot of the sample using a hot electron capture datector (ECD) and argon-methane carrier gas. Typical relative standard deviations of the calculated results are 0.04% for carbon dioxide, 0.4% for methane, and 0.3% for nitrous oxide.