The paper presents a theoretical study of sorption properties of submicroporous elastic materials. The effect of submicropore size upon the energy of sorption is exposed. Formulas for energy and entropy changes due to the sorption in properly defined subsystems are derived. The resultant model consists of a set of nonlinear equations representing the sorption isotherms for the subsystems (multiple sorption model). By solving the equations for a given relative pressure of sorbate, one obtains the sorption capacity of each subsystem, so the total sorption isotherm can be found. Some alternative assumptions are discussed, and corresponding models are examined. Exemplary theoretical isotherms are shown and compared with empirical data (coal-H2O, Coal-CH4, coal-C6H6). The model may be used for a qualitative analysis of empirical sorption isotherms to verify some hypotheses about the sorbent structure and mechanisms of the sorption process.