An ultracentrifugation sedimentation technique was developed utilizing FT-IR spectroscopy to measure semi-quantitatively the adsorption of surfactants onto small colloidal dispersions in hydrocarbon solutions. This technique was used to characterize the aggregation behavior of two classes of oil-soluble lubricant additives, basic calcium phenates and poly(isobutenyl)succinimide dispersants. It was demonstrated that calcium phenates containing oil-solubilized calcium carbonate form small colloidal dispersions in non-aqueous solvents. Self-association of certain derivatized poly(isobutenyl)succinimide dispersants containing hydroxyl functionalities was also observed. In addition, adsorption of poly(isobutenyl)succinimide dispersants onto basic calcium phenate colloidal dispersions was semi-quantitatively measured using the line-start ultracentrifugation sedimentation profile technique. Succinimide adsorption was shown to occur through interaction of the polar dispersant headgroup with the calcium phenate colloid. Factors affecting succinimide adsorption were characterized, including the effect of the polyalkenyl polyamine chain length, polyisobutylene molecular weight and derivatization with hydroxyacetic acid.