The capability of molecular simulation, combined with pore-size distribution (PSD) analysis, to predict adsorption equilibrium in microporous carbon adsorbents, using as a case study the adsorption of methane and ethane, was investigated. The calculations indicate that a wide range of data for the adsorption of pure components and binary mixtures can be predicted successfully. Significantly, only a limited set of experimental data comprising three or four adsorption measurements is required to calculate the PSD. This predictive ability is relevant to both the design of adsorptive separation processes and the design of new adsorbents.