AbstractThe tribological properties of three representative antiwear and extreme‐pressure additives, tricresylphosphate (TCP), triphenylthiophosphate (TPPT), and α‐mercaptobenzothiazole (MBT), in pentaerythritol ester at different concentrations were studied. It was found that TCP could react with Fe to form an organic phosphate film containing 4% P on the scar surface, while TPPT formed a blended organic phosphate and inorganic FeS film, containing 4% P and 6% S, respectively. MBT formed an inorganic FeS film containing 45% S. Ferrographic analyses of wear particles collected from oil samples after four‐ball tests showed that the higher the temperature the better the tribological performance of the additivated ester, due to its reaction with the metal s