Methods for blending fuels

A method for preparing a refinery fuel composition for a spark-ignition internal combustion engine, the refinery fuel composition having a target octane number, said method comprising:

• blending two or more refinery streams and optionally one or more fuel additives 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;
• (ii) testing the octane number of the refinery fuel composition;
• and
• (iii) blending the refinery fuel composition with an octane-boosting additive in an amount sufficient to increase the octane number of the refinery fuel composition to at least the target octane number;
• wherein the octane-boosting additive has the following formula:
• where:
• R1 is hydrogen;
• R2, R3, R4, R11, and R12 are each independently selected from hydrogen, alkyl, alkoxy, alkoxy-alkyl, secondary amine and tertiary amine groups;
• R6, R7, R8 and R9 are each independently selected from hydrogen, alkyl, alkoxy, alkoxy-alkyl, secondary amine and tertiary amine groups;
• X is selected from —O— or —NR10—, where R10 is selected from hydrogen and alkyl groups;
• and
• n is 0 or 1.