An aviation gasoline composition comprising an impure iso-octane fraction, at least one xylene and at least one C4 or C5 alkane, wherein the impure iso-octane fraction in said composition is a fraction comprising at least 90 mol % iso-octane and having a final boiling point of at least 180° C. and is present in the composition in an amount in the range of from 30 to 80 vol. % based on the composition, the composition is substantially free of any lead compounds, the composition has a motor octane number of at least 94 and the composition has a final boiling point of at most 170° C. The composition of the present invention may be made by blending together an impure iso-octane fraction, xylene, at least one C4 or C5 alkane, optionally ethyl tertiary butyl ether, and optionally methylcyclopentadienyl manganese tricarbonyl and may be used in a spark ignition aviation engine, either alone or in combination with methanol or a methanol and water mixture.