An additive composition for a fuel comprises: (i) a metal compound selected from an iron compound, a manganese compound, a calcium compound, a cerium compound and mixtures thereof; (ii) an organic compound selected from a bicyclic monoterpene, substituted bicyclic monoterpene, adamantane, propylene carbonate and mixtures thereof; and (iii) a stabiliser. The additive composition allows fuels which are prone to separation, for example blended fuels or fuels having a high content of asphaltenes, to be used successfully.