The experimental adsorption and desorption equilibrium data for propane, propylene, and propane-propylene mixtures on 13X molecular sieves are presented for different temperatures and compositions; these data were efficiently determined by using the differential sorption bed system described by Liapis et al. (Sep. Technol. 1992, 2, 141-154). The Toth equation was found to correlate with the experimental equilibrium single-component data very well. For the binary propane-propylene mixtures, propylene is the most preferentially adsorbed component. The feasibility of describing the experimental binary equilibrium data with the ideal adsorbed solution expressions, the heterogeneous ideal adsorbed solution expressions and the heterogeneous ideal adsorbed solution with specific gas-solid interactions expressions was examined. Comparison between these expressions and the experimental binary equilibrium data showed that none of the expressions could satisfactorily describe the experimental results for the binary mixtures for all temperatures and compositions studied in this work. For a given multicomponent adsorption system of interest, numerous sets of experimental equilibrium data of adsorption and desorption could be efficiently and accurately determined by using the differential sorption bed system and the experimental procedures described in this work; these results could be used in parameter estimation and model discrimination studies, as well as in process design.