Superfuels: are they worth the money? - Our tests

We compared both petrol and diesel products to determine their benefits, and used several cars to assess their performance - including a Ford Focus 1.6 to compare petrols, and a VW Golf 1.9 TDI for diesels.

We also carried out a longer-term economy test with a Ford Focus 1.4 petrol, because BP claims you only start to see the real economy gains after three tankfuls of Ultimate.

To test performance claims, we tested acceleration in each car from 30-70mph through the gears and in fourth gear alone.

To see if premium products yielded any benefits for a performance car, we compared Shell 95 and 99 V-Power directly in a Volkswagen Golf GTI.

The tests, carried out by the AA's former senior research engineer Peter de Nayer, were rigorous. De Nayer replicated 'real world' driving, ensuring consistent conditions for each test.