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Previously reported tests (SAE 2005-01-3839) suggest that lubricant oxidative stability can be improved by running a spark ignition engine with fuels rich in light olefins (e.g. from a catalytically cracked refinery stream). To further our understanding, we have modelled the influence of fuel chemistry on the kinetics of lubricant oxidation. In the hypothesis presented here, the olefins interfere with key chain branching reactions in the lubricant oxidation process and react to form epoxides, which are sufficiently volatile to leave the lubricant. The modelling also predicts that ethanol has a directionally beneficial effect on lubricant oxidative stability. The effect of this will be limited because ethanol is much less soluble in lube-oil under prevailing engine conditions than heavier hydrocarbon components.