High-pressure adsorption of methane, carbon dioxide, and nitrogen on zeolite 13X was measured in the pressure range (0 to 5) MPa at (298, 308, and 323) K and fitted with the Toth and multisite Langmuir models. Isosteric heats of adsorption were (12.8, 15.3, and 37.2) kJ/mol for nitrogen, methane, and carbon dioxide respectively, which indicate a very strong adsorption of carbon dioxide. The preferential adsorption capacity of CO2 on zeolite 13X was much higher than for the other gases, indicating that zeolite 13X can be used for methane purification from natural gas or for carbon dioxide sequestration from flue gas.