Possibilities of Integral Equation (IE) Approach to study the mixed-gas adsorption equilibria are considered. Generalization of Dubinin-Astakhov equation for the case of mixed-gas adsorption is presented and the corresponding expressions for isosteric heats of adsorption are obtained, taking into account the interactions between adsorbed molecules. To predict phase diagrams and isosteric heats of mixture components only the knowledge of single-gas isotherm adsorption and accompanying calorimetric effects are required. A special attention is given to possibilities of arriving at relatively simple analytical or combined analytical/numerical solutions.