Superfuels: are they worth the money? - How we did our fuel tests

Our tests were carried out by Peter de Nayer, who invented the AA's own fuel economy tests in the '80s.

To calculate economy he uses a special meter in the fuel line to measure the precise amount of fuel used on a series of road routes.

For each fuel, five sets of results - for urban driving, suburban driving, brisk driving out-of-town, motorway driving and gentle driving - were taken and used to calculate a rounded 'real world' average figure.

All driving was carried out at night, to reduce the effects of different traffic conditions.

The urban test took 11.3 minutes at an average speed of 17mph and included 12 stops, as well as three 'street corners' taken at 10mph, and brief periods of cruising at 30mph and 40mph.

The car was stationary for 180 seconds in total - 26.5% of the time.

Next was gentle driving, including a cold start (at 10C) and was a typical 20-mile trip on winding, rural roads, with a maximum cruising speed of 40mph and an average of 30mph.

It included 10 brief halts at junctions, hillclimbs and descents.

The average is calculated by adding together 10% urban, 15% suburban and 25% each for motorway, brisk driving out-of-town and the gentle drive.