Misleading dross. For a long time now car manufacturers have been forced to use Super to get the best possible performance out of their engines for emissions tests and I can tell you for a fact that all current engines are optimised for the best fuels for this reason. Higher RON petrol and higher Cetane diesel provide more torque at low rpm allowing for earlier upshifts (even with automatic transmissions) so that alone slightly improves economy. It's also true that the engines produce around 10% more horsepower at higher revs that most drivers never even get to. Branded Super also contains packages of additives to lubricate fuel systems and helps keep the valves (especially in DI engines) clear of carbon build up.