It has been reported that the middle range of gasoline distillation temperatures strongly affects vehicle driveability and exhaust hydrocarbon (HC) emissions, and that MTBE(CH3-O-C4H9)- blended gasoline causes poor driveability during warm-up. The present paper is concerned with the results of subsequent detailed research on gasoline characteristics, exhaust emissions and driveability.In this paper, first it is demonstrated by using four models of passenger cars having different types of exhaust gas treatment system that decreased 50% distillation temperature (T50) reduces exhaust HC emission. This result indicates lowering T50 in the market will contribute to improving air quality.Secondly gasoline behavior in the intake manifold is investigated by using an engine on the dynamometer in order to clarify the mechanisms of HC emission increase and poor engine response which are caused by high T50. It is found that high T50 cause poor gasoline vaporization and increased remaining liquid gasoline in the intake manifold, and this results in increased HC emission and poor engine response.MTBE-blended gasoline deteriorate driveability by combination of following relations; MTBE content in the mixture of warm-up engines increases more than that of original MTBE-blended gasoline. MTBE has low calorific value. MTBE-blend causes lean mixture because of oxygen containing.