This 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 Xray photoelectron spectroscopy f l P S ) 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 conditions.