Fuel compositions with additives

A fuel composition for a spark-ignition internal combustion engine, the fuel composition comprising a non-metallic octane-boosting additive and a base fuel, wherein the non-metallic octane-boosting additive has the formula:

• where:
• R1 is hydrogen;
• R2, R3, R4, R5, R11 and R12 are each independently selected from hydrogen, alkyl, alkoxy, alkoxy-alkyl, secondary amine and tertiary amine groups;
• R6, R7, R5 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,
• wherein at least one of R2, R3, R4, R5, R6, R7, R8, R9, R11 and R12 is selected from a group other than hydrogen;
• and
• wherein the non-metallic octane-boosting additive, when used at a treat rate of 0.67% weight additive/weight base fuel, increases the research octane number of a fuel by at least 1.8 without increasing:
• the T90 by more than 2.5%;
• or
• the vapour pressure by more than 2.0%.