The purpose of this work was to develop a series of octane reference fuels for road testing methanol fueled vehicles. Preliminary attempts to measure the research octane number of neat methanol by the standard ASTM test procedure produced anomalous results. This led to a more basic method of measuring the octane number based on the incipient knock compression ratio. The incipient knock method gave research and motor octane numbers of 112 and 88, respectively, for neat methanol. Research octane numbers of several methanol reference fuel blends prepared by adding octane enhancers and depressors were determined. The effects of spark timing and air/fuel mixture temperature on the incipient knock compression ratio of neat methanol were also examined.