This study was undertaken to determine the vapor pressure characteristics of M85 fuel, a mixture of 85 percent methanol and 15 percent gasoline or other hydrocarbons. For M85 fuels made with full-boiling-range gasolines, the vapor pressure of the M85 fuel at 37.8°C increased linearly with an increase in the vapor pressure of the gasoline. A different linear relationship was obtained for M85 fuels made with pure hydrocarbons rather than with gasolines. The vapor pressure of an M85 fuel was higher when the hydrocarbon component was a pure hydrocarbon or simple hydrocarbon mixture rather than a gasoline of the same vapor pressure.Vapor pressure vs. temperature characteristics were measured for a number of M85 fuels and the hydrocarbons from which they were made. In most cases, a change in temperature caused a greater change in the vapor pressure of the M85 fuel than in the vapor pressure of the hydrocarbon component of the M85.