Experimental adsorption isotherms of pure carbon dioxide, ethylene, and propane as well as their mixtures have been obtained on three samples of ZSM-5 zeolite of different atomic Si/Al ratios (15, 29, and 60) over the pressure range 0-100 kPa. The data-are given at temperatures of 281, 293, and 308 K (pure data) and 293 K (binary and ternary data). Changes in the zeolite selectivity with its Si/Al ratio were observed for the pure components, with an increase in the loading of polar molecules, like carbon dioxide and ethylene, as the atomic Si/Al ratio decreases. The selectivity, however, was nearly constant for propane. The characteristic equilibrium curve was obtained for each adsorbent, and a good fit of the equilibrium data was obtained for all adsorbates at the three temperatures. Some equilibrium overadsorption and displacement effects with large deviations from the ideal behavior-including binary azeotropes-were found for the mixtures of polar and nonpolar compounds. Thus, ethylene and carbon dioxide are displaced by propane, showing a maximum in their individual adsorption isotherms in the binary mixtures. The Si/Al ratio of the zeolite was found to modify the azeotrope and overadsorption effects.