AbstractExtending automotive engine drain intervals requires a good knowledge of the antiwear aspect of lubricant performance, which is often closely linked to the oxidative degradation of the oils. In this paper, we report the physicochemical analyses and tribological tests carried out on several oils oxidised by laboratory oxidation tests at different stages. An interesting correlation was found between the antiwear efficiency and some characteristics of the eletrochemical impedance spectra of such oxidised lubricants. A promising way of understanding the mechanisms of wear mitigation by aged engine oils is proposed.