A method for preparing a refinery fuel composition having a target octane number, comprises: (i) blending fuel components in proportions which are designed to give a refinery fuel composition with an octane number which is greater than the target octane number by a margin of less than 1; and (ii) testing the octane number of the refinery fuel composition and, if the octane number falls below the target octane number, blending the refinery fuel composition with a non-metallic octane-boosting additive. A further method comprises: (a) passing a first refinery fuel composition comprising a non-metallic octane-boosting additive to a fuel handing system, and discharging the first refinery fuel composition from the fuel handing system; and (b) passing a second refinery fuel composition to the fuel handing system.