Data on the behavior of crude oil n-pentane- and n-heptane-insoluble fractions in aromatic solvent systems were obtained. Surface and interfacial tensions in systems formed by Brazilian crude oil n-pentane insolubles (C5I) and n-heptane insolubles (C7I) in the aromatic solvents toluene, pyridine, and nitrobenzene were measured at, room temperature using the ring method and employing an automatic tensiometer, The results indicated possible asphaltene aggregation as well as the probable existence of critical micelle concentrations for both C5I and C7I fractions in each of the three solvents considered. Critical micelle concentrations measured for the C5I fraction in toluene and pyridine solutions were consistently higher than those in systems containing the C7I fraction, indicating a lower association tendency in the C5I fraction. Average molecular areas for asphaltenes adsorbed at different interfaces estimated from surface tension measurements were found to be in agreement with literature values and appeared to suggest a planewise surface adsorption of asphaltene molecules, which is consistent with currently accepted stacking aggregation mechanism of asphaltenes. The presence of a discontinuous point for the kinematic viscosity of asphaltene/toluene solutions as a function of asphaltene concentration suggested yet another type of aggregation of asphaltenes at concentrations higher than the observed cmc in toluene.