A gas chromatographic method was developed for the rapid separation of headspace gases in film-package of fresh produce. A balanced set of three columns simultaneously separated four gases including N2, O2, CO2 and Ar. The gas composition was accurately calculated by measuring the ratio of each peak area on the chromatograms and considering the relative response of a thermal conductivity detector to each gas. This method was found to be useful for the accurate determination of O2 and CO2 in the modified atmosphere, because Ar proved to be kept in film packages of the produce at a concentration above ca. 0.9% in various cases while Ar overlaps O2 on the gas chromatograms in conventional gas chromatographic systems.