The theoretical prediction of multicomponent adsorption equilibria from the single-component data is one of the most important problems in adsorption. The possibilities of the ideal adsorbed solution approach to study enthalpic effects accompanying the mixed-gas adsorption equilibria are presented. The obtained theoretical expressions for predicting isosteric heats of adsorption in a gas mixture are relatively simple and accurate. To predict phase diagrams and calorimetric effects in the mixed-gas adsorption, only the knowledge of single-gas adsorption isotherms and accompanying calorimetric effects is required.