The paper presents the results of research on possible application of an original clustering based mathematical description of gas adsorption processes to analysis of microporous structures of activated carbons. The LBET class model used is based on the classical BET approach to the multilayer adsorption process modelling, but it takes into account geometrical restrictions for the clusters size and a geometrical and energetic heterogeneity of surface. The effects of adhesive forces on the creation of second and higher layers are handled explicitly. An original fluid statemodel is used to make calculations possible for gas adsorption isotherms. Fitting of the LBET model to the empirical data is proposed to detect active constraints for multilayer adsorption and so to get information on the structure of micropores. Application of the formulae to the analysis of nitrogen and methane isotherms on an active carbon is discussed. (C) 2010 Elsevier B.V. All rights reserved.