The structural and energetic heterogeneity of silica gel and pyrocarbon/silica gel adsorbents was studied by means of the adsorption methods. The properties of polyethylene glycols (PEG 4000, PEG 1500) in a mixture with the solid adsorbents have been investigated using different probe molecules for gas chromatography. The carbosils investigated possessed a mosaic structure due to carbon deposit distribution features. The mechanism of formation of polyethylene glycol layers on the carbosils surface depends on the chemical structure and amount of pyrocarbon. Chemical and structural heterogeneity of the adsorbent surface is of great importance in this case. From the practical point of view, it was interesting to study the effect of such heterogeneity on the selectivity of the chromatographic columns in relation to the model mixtures.