A model of equilibrium separation of gas mixtures was used to describe steps of pressurization and cocurrent desorption. Relationships taken from the model were compared with experimental data obtained at desorption step for carbonaceous adsorbents with various porous structures. A method that allows the differentiation of adsorbents＇ separation properties and the evaluation of their suitability in enrichment of methane/nitrogen mixtures by pressure swing adsorption technique is given.