Theoretical foundations for the comparison of adsorption isotherms at the range of low surface coverages are presented in order to facilitate the use of this high-resolution comparative analysis for characterization of porous adsorbents. The well-known models of adsorption on heterogeneous and microporous solids were used to explain the different types of the high-resolution comparative plots observed experimentally. As expected, the presence of micropores contributes mainly to the upward curvature on the high-resolution plot, but this curvature can be enlarged or reduced significantly by the difference in the surface properties of the compared adsorbents. It is shown that a proper selection of the reference solid allows a quantitative characterization of microporosity and surface heterogeneity of porous adsorbents.