In this work, the adsorption equilibrium isotherms of carbon dioxide, methane and nitrogen on Na- and H-mordenite at three temperatures (279, 293 and 308 K) for pressures up to 2 MPa have been obtained. For Na-mordenite, the selectivity order is: carbon dioxide >> methane > nitrogen. The selectivity order is the same for H-mordenite, although the selectivity ratio CO2/CH4 is smaller and the CH4/N-2 ratio is larger, the latter being due to the lower affinity of nitrogen to H-mordenite. All the isotherms can be reproduced adequately with the Toth model, including the effect of temperature on the model parameters. The adsorption capacity for methane and nitrogen is recovered with vacuum in both adsorbents, whereas this does not apply to carbon dioxide for Na-mordenite. H-mordenite offers selectivity ratios higher than 3 at subatmospheric pressures for carbon dioxide/methane, carbon dioxide/nitrogen and methane/nitrogen mixtures, making this adsorbent suitable for the separation of these mixtures by a vacuum swing adsorption process. (c) 2005 Elsevier B.V. All rights reserved.