A correlating equation for liquid-phase adsorption equilibria, including the effects of temperature and pore diameter, is presented, together with a derivation of the equation ascribing the equilibration process of physical adsorption to van der Waal's forces. The derivation is based on the effect of temperature and surface configuration on the concentration of adsorbate at the surface. The correlating equation was tested with experimental data for the benzene-cyclohexane-silica-gel system and the toluene-isooctane–silica-gel system. Temperatures ranged between 23.9° and 99°C. and the pore diameters between 20.7 and 149.5 Å.