The investigated materials were the bitumens produced from naphthenic (Venezuelan) and paraffin-naphthenic (Uralian) crude oils by different technological methods. The bitumens of 70 and 50 pen were analyzed for generic composition, macrostructure and colloidal stability. The size of asphaltene micelles and the extent of their aggregation were influenced by the chemical type of the feedstock and the method of bitumen production. SEM examinations of asphaltenes made it possible to discern micelles ranging in size from 110 to 260 nm. Examinations of Uralian bitumens revealed particles of a smaller size as compared to those of the asphaltenes from Venezuelan bitumens, but the extent of aggregation was greater for Uralian asphaltenes. Air-blowing increased the extent of aggregation of asphaltene micelles. Fractionation of asphaltenes and analysis of bitumens by the GPC method showed a higher content of the heaviest components in bitumens, which were subjected to a more intensive oxidation. The bitumens under study exhibited a satisfactory colloidal stability. The slightly higher colloidal stability parameter of bitumens from naphthenic crude oil is likely to be due to a smaller aggregation of asphaltene micelles and a greater resins to asphaltenes ratio in these bitumens. (C) 2003 Elsevier B.V All rights reserved.