AbstractThis paper describes a study of the effect of aromatics in lubricant base oils on the efficiency of adsorptive additives in terms of lubrication and rust‐inhibition performance. The additives investigated were sulphurised isobutylene, tricresyl phosphate (TCP), sorbitol monooleate (Span‐80), and alkylene succinic acid. Four‐ball friction and wear tests, a modified ASTM D 665 rust test, an electrochemical test, and X‐ray photoelectron spectroscopy (XPS) were used to reveal the relationship between the aromatics and the additives. The results show that the aromatic hydrocarbons in the base oils reduce the surface activity of the additives; competitive adsorption between the polar compounds and the additives is not a key factor governing the behaviour of the additives under the test con