The engine fuel efficiency is tested based on two distinct set of driving conditions. The first is the urban cycle which is meant to test city fuel economy. The second is the extra urban cycle which is meant to test highway fuel economy and country driving fuel economy. The urban cycle does not exceed 31 miles per hour and features accelerations, decelerations and idling over and 2.5 mile track. The extra urban cycle does not exceed 75 miles per hour with accelerations and decelerations over a 4.3 mile track. The top mpg of both tests is combined and weighted to work out the combined fuel economy mpg figure.

The fuel usage and fuel type has a bearing on the Co2 emissions which traditionally are lower for diesel cars. The Co2 emissions are used to work out the car tax band for the vehicle.

All car manufacturers must have the test done to show the car mileage and petrol consumption on a label which is fixed on all new cars for sale. This way potential owners can consider a vehicle list not only by car description and car make but they can also rank cars by mpg.