To identify hydrocarbon components suitably blended in the M85 (Methanol : 85 vol%, Gasoline : 15 vol%) fuel while maintaining high emission control performance of the catalyst, the effects of various hydrocarbons on the methanol conversion efficiency were investigated. Saturated hydrocarbons having about 5-7 carbon atoms did not inhibit the methanol conversion efficiency. In contrast, unsaturated hydrocarbons and aromatic hydrocarbons inhibited the methanol conversion efficiency. It was concluded that low saturated hydrocarbons such as light-naphtha were suitable for hydrocarbons mixed with methanol fuel.