The structural and rheological properties of resin-free model petroleum mixtures (MPM) with an asphaltene content of 0 to 6 wt % and the same mixtures with added 3.85 wt % petroleum resins have been investigated. The composition of the mixtures simulates the amount of the main hydrocarbon-group components and distillate fractions in light paraffin-base oils (rho(4) (20) = 747.7-789.1 kg/m(3)). Temperature-dynamic viscosity relationships for cooling the MPM have been obtained, most of which displayed abnormalities in the temperature range of similar to 40-60A degrees C. Calculations of the viscous-flow activation energy (E (mu)) have shown that there are abrupt changes in E (mu) in this abnormality region, which are an indication of structuring processes. By means of Fourier-transform laser diffractomery of MPM solutions in kerosene, it has been found that the particle size of the petroleum mixtures is qualitatively related to the revealed abrupt changes in E (mu). It has been shown that these abnormalities correspond to the formation of paraffin-asphaltene associates and their existence is determined by the critical concentration of resins and asphaltenes in the mixtures.