The gc analysis procedures for the determination of the products of the catalytic oxidation of n-butenes and n-butane are presented. The analytical problems were solved by on line and pseudo on line methods depending on the reaction mode. The calibration of the gc estimation of maleic anhydride and some factors influencing the accuracy of the determination of this compound were thoroughly studied. It could be shown that the analytical methods developed using packed columns provide precise data at sufficiently short times of the analyses.