Adsorption data of single, binary, and ternary mixtures of methane, ethane, and ethylene on Silicoalumina-Phosphate molecular Sieve (SAPO-34) were obtained experimentally in the pressure range of 0 to 600 kPa at 303, 313, and 323 K. The adsorbed equilibrium concentration was predicted based on the vacancy solution theory (VST) using excess Gibbs energy (EGE) models of activity coefficients. EGE models were studied comparatively, i.e., the Wilson, Flory Huggins, and NRTL equations. The VSM-model results were compared with the mixture adsorption data. The results revealed higher capability of EGE models against the extended Langmuir equation in predicting adsorption behavior of the so-called gas mixture.