To obtain a gasoline which is excellent in engine output characteristics and can decrease the amt. of a heavy arom. hydrocarbon fraction compounded and the amt. of harmful substance in an exhaust gas by mixing methylcyclopentane into a gasoline.

Two (2)-95vol.% methylcyclopentane is mixed into a usually used gasoline base. Thus, the flame speed and engine output are greatly improved in comparison with isooctane alone or a gasoline contg. cyclohexane or hexane, and the effects similar to those of a gasoline contg. benzene are obtd. The amt. of harmful substance (e.g. benzene) in an engine exhaust gas is not largely different from that derived from isooctane alone or a gasoline contg. hexane, is markedly smaller than that derived from one contg. cyclohexane or cyclohexene, and is about 1/19 of that derived from one contg. benzene.