In this paper we discuss the expression for the total retention volume, treated as a pressure function, and the analytical methods for determination of the energy distribution function directly from gas-adsorption chromatagraphy data. It is shown that by assuming Jovanovich and Langmuir local behavior for the adsorbed phase, the total retention volume may be expressed as Laplace and generalized Stieltjes transforms, respectively. The utility of our theoretical considerations is demonstrated for the hexane-Polsorb C adsorption system.