The possibilities of the non-ideal adsorbed solution approach to study enthalpic effects accompanying mixed-gas adsorption equilibria is presented. The model of calculations take into account the surface energetic heterogeneity and the effects of the lateral interactions between adsorbed molecules by using Flory-Huggins activity coefficient equations. The theoretical expressions for predicting isosteric heats of adsorption in the 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. (C) 2003 Elsevier B.V. All rights reserved.