gents... actually the new Shell Super with Fuel Economy formula uses their new Synthetic Viscous Friction Improver (SVFI). Basically, how it works is that the new additive is not combustible during power stroke, and therefore acts as an agent to smoother the movement of your piston. As you already know, engine oil lubricates the piston and the engine block, not the combustion chamber. So, SVFI is suppose to help drivers to achieve better mileage by this mechanism.
John and Helen Taylor, the couple who used a stock Volkswagen Golf 1.6 FSi travelled across 25 countries (28000 kilometers approximately) using only 1303 litres of Shell Super OR 24 full tanks. average fuel consumption was 22.2 km/litre.
Along with them during this world record attempt, were officers from Guinness Book World Of Record to witness the whole event.
So, folks, yes, with 1 fill up, you may not notice the difference, but you should get better mileage from 2nd fill-ups onwards.
ANyhow, all of these depends very much on your driving style...
if u happen to have a very heavy right foot, the new Shell Super with Fuel Economy Formula will not help.
Cheers bros!