Abstract: The present invention relates to a method of blending a multi-component blended fuel. The method comprises selecting as a starting reference a known multi-component blended fuel (e.g. a blend of gasoline and ethanol) which is in use by an internal combustion engine which operates SI or HCCI combustion. The method comprises blending an alternative fuel which can be used by the same engine without modification of the engine, including without modifying the operating regime employed by its engine management system. The alternative fuel is a blend comprising all of the components of the known fuel and an additional fuel component (e.g. methanol). The blend components are blended in proportions which give to the alternative fuel: a stoichiometric air-fuel ratio by mass or by volume substantially equal to that of the known blended fuel; and/or a lower heating valve (e.g.