Various theories based on the assumption of an adsorbed solution in order to predict multicomponent gas adsorption equilibria are presented. In detail the Ideal Adsorbed Solution Theory (IAST), the Heterogeneous Ideal Adsorbed Solution Theory (HIAST), the Multiphase Ideal Adsorbed Solution Theory (MIAST), the Spreading Pressure Dependent Model (SPDM), the Predictive Real Adsorbed Solution Theory (PRAST), and the Vacancy Solution Model (VSM) are described. Applying these models to predict multicomponent adsorption equilibria for selected examples, in case of nonideal adsorption behaviour with positive deviations from Raoult＇s law no model was able to achieve satisfactorily aggreement with experimental data.