This paper consists of three main parts. In the first part, the new model isotherm equations for adsorption on heterogeneous microporous solids are presented, using different (and never before utilized) pore-size distribution functions. In the second part, freshly developed adsorption isotherms are applied to check the power of the CONTIN algorithm. Finally, in the third part, the micropore-size distributions (MPSD) of two strictly microporous activated carbons (of synthetic origin) are calculated on the basis of different adsorption models and numerical methods of solving the global adsorption isotherm equation. The following methods are put to use: the recently developed gamma-type adsorption isotherm (GTAI) equation, applied for the first time in adsorption studies, the modified Galerkin method, CONTIN, and, finally, the density functional theory. The usefulness of CONTIN and the similarities between the results of the applied methods are discussed. The influence of the heterogeneity parameter (n) of the Dubinin-Astakhov equation as well as the relation between characteristic adsorption energy and pore diameter on the shape and position of the MPSD is considered. Some remarks on the optimization process of fitting GTAI to experimental data are also given.