The invention relates to a determination of end of life of oil by electrical means. Electrical measures of resistivity and permittivity of engine lubricating oil are gathered continuously under normal vehicle engine operating conditions and combined into a composite parameter, the aggregated electrical measure, which, is indicative of engine oil condition and when plotted over the useful life of the oil displays a first linear slope anticipatory of the end of oil life followed by a second, steeper slope indicative of the end of oil life. An algorithm, implementable in an on-vehicle computer, to reliably detect these features is described.