Gas-liquid chromatography is the main analytical method in petroleum chemistry. An equation has been obtained for the retention volume (with account taken both of absorption and of adsorption contributions), which describes the dependence of the retention volume on the pressure and nature of the carrier gas for the actual sorbent under gas-liquid chromatography conditions. Means of practical application of;the equation obtained for determining physicochemical quantities have been examined. An equation has been derived for the degree of separation, which takes account of the dependence of the degree of separation on the pressure and nature of the carrier gas and indicates the possibility of the latter having a considerable influence on the process of chromatographic separation of complex mixtures in petroleum chemistry.