The effects of methanol/gasoline mixtures on swell properties and tensile properties of selected automotive elastomers were investigated. Two gasolines with aromatic contents of 30% and 50% were used in the investigation. Equilibrium swell measurements and tensile measurements were conducted using ASTM standard procedures. The results show that although few elastomers were affected drastically by pure gasoline (e.g. natural rubber) and a few by methanol (e.g. fluorocarbon elastomer) most of the elastomers were more severely affected by mixtures of the gasoline and methanol rather than the pure components. Presence of higher aromatic content in the methanol/gasoline mixtures led to additional deterioration of properties. The data on all elastomers except the fluorocarbon can be explained in terms of the solubility parameter concept.Ultimate tensile and ultimate elongation values of elastomer networks were found to be quantitatively related by simple linear equations to the volume fraction of rubber in the swelled networks. They were also found to fit equations derived for equilibrium stress-strain relationships.