A detailed chemical kinetic modeling study was undertaken to characterize the auto-ignition behaviour of a full range of blends of both methanol and ethanol with a PRF 80 base fuel. The overall results were encapsulated in a computationally efficient semi-empirical formulation. The auto-ignition model was combined with an ASTM (CFR) engine simulation to explore the underlying causes for the octane number value exhibited by alcohol fuels. The model predictions were validated against experimental pressure traces obtained with a range of alcohol-PRF blends. These results confirmed the model's general validity and provide valuable insights relating to the controlling role of the cool flame in the octane number determination and the use of alcohol fuels as octane blending components for use in modern and future gasoline engine technologies. (C) 2009 Elsevier Ltd. All rights reserved.