The tie line and liquid-liquid equilibrium data are presented for mixtures of an alkanol + hept-1-ene + water at 25-degrees-C. The data are compared to the related mixtures of an alkanol + heptene + water at 25-degrees-C. The alkanol refers to all the C1, C2, C3, and C4 alcohols. The measurements have a bearing on the water contamination problem inherent in gasoline + alcohol blends.