Transient adsorption process of a hypothetical ternary mixture constituted by a fast diffusing-weak adsorbing (C1), a low diffusing-strong adsorbing (C2), and a high saturation capacity species (0) on zeolite adsorbents in a batch system was modeled by the Maxwell-Stefan formulation in combination with the IAST mixture isotherm. When the Henry constant of C2 and C3 were K-2 = K-3, the transient adsorption selectivity (S-i,S-j) defined with the weakest-adsorbing species used as a reference becomes higher for C3 in comparison with C2, during the entire lapse of contact time. The influence of the gas phase pressure and mixture composition on the transient adsorption selectivities basically depends on the behavior of the equilibrium selectivities (S-i,j(eq)). The transient response of the fractional coverage (theta(i)) of C1 within the zeolite overshoots its equilibrium value. In comparison to the single adsorption profiles, the component with the highest saturation capacity (C3) is the only species of the ternary mixture that maintains its fractional coverage practically unmodified. When K-2>K-3, a cross-over between the corresponding equilibrium selectivities can occur with pressure. The use of the model based on experimental data is discussed.