A new kinetic equation is proposed which describes the diffusional process in the system hard coal-gases, in isothermal-isobaric conditions. This equation ij illustrated by its practical application to the sorption of CO:! and CH4 on one type of highly metamorphised coal. The kinetic model considered in this paper enables an attempt at the analysis of the equilibrium states depending on changes in the specific surface areas of coal grains. The results of the considerations of the model are compared with the experimental kinetics of nitrogen sorption on type A zeolite. Relations with Fick＇s II law are demonstrated