This paper examines the relative flammability hazard presented by the fuel tank headspace vapors of various alcohol-gasoline blends, including methanol (M100), ethanol (ElOO), winter gasoline, summer gasoline and winter and summer blends of M85 E85, and E10. Ignition tests were conducted to establish flammability limits for each of the fuels. Measured limits were compared to those predicted by the RMC multicomponent fuel volatility model and conclusions were drawn as to the comparative hazards of the fuels studied. The model was also used to examine the effect of fuel tank fill level on the flammability limits of the respective blends. The results show the tendency of the flammability limits both to broaden and shift to warmer temperatures with decreasing fill level or increasing alcohol content.