Adsorption equilibria of CH4 and N-2 On activated carbon and silica gel were measured for a wide temperature range covering the critical point: 158-298 K for CH4, and 103 298 K for N-2. The determination of the compressibility factor is shown to have considerabie effect on isotherm behavior at conditions after the isotherm maximum. A change in adsorption mechanisms on crossing the critical temperature was observed in all cases. The kind of adsorbents and how far the equilibrium temperature to the critical one are major factors affecting the transition of isotherms from sub- to supercritical. All continuous isotherms can be modeled by a unique model for the supercritical region. The satisfactory fitting of the model to the experimental isotherms proved the reliability of the absolute adsorption determined by the proposed method.