To study the relationship between structure and properties of members of the lipidic thiobis phenol series, as extreme pressure additives in lubricants, a series of homologous compounds has been synthesised by the reaction of alkylphenols with sulphur dichloride. The isomeric n-nonylphenols have been reacted to form the C9 isomeric 2,2¢-and 4,4¢-thiobisphenols. Longer alkyl sidechains resulted mainly in the formation of 4,4¢-thiobisphenols and some of the 2,2¢ isomer. With short alkyl, particularly t-alkyl side-chains, steric hindrance resulted in the 2,2¢-compound. Additive studies have indicated that the longer chain 4,4¢ compounds possessed antioxidant properties comparable and superior to former commercial branched chain 2,2¢ compounds produced from petrochemical intermediates.