That's phenomenal. And I thought I'd done well to get 41mpg over 700 miles in a Jag XJL 3.0V6 diesel limo. Here's how the EC tests fuel economy and CO2. Note no account of fuel used to regenerate DPFs. And tests done at between 20C and 30C when all engines will be at their most efficient and will even start from warm:Imperial urban fuel consumption (mpg) (cold) The urban test cycle is carried out in a laboratory at an ambient temperature of twenty degrees Celsius to thirty degrees Celsius on a rolling road from a cold start, ie the engine has not run for several hours. The cycle consists of a series of accelerations, steady speeds, decelerations and idling. Maximum speed is 31 mph (5 km/h), average speed 12mph (19km/h) and the distance covered is 2.5 miles (4km). Imperial extra-urban fuel consumption (mpg) The extra-urban cycle is conducted immediately following the urban cycle and consists roughly half steady speed driving and the remainder accelerations, decelerations and some idling. Maximum speed is 75mph (120km/h), average speed is 39mph (63km/h) and the distance covered is 4.3 miles (7 km). Imperial combined fuel consumption (mpg) The combined figure presented is for the urban and the extra-urban cycle together. It is therefore an average of the two other parts of the fuel consumption test, urban and extra-urban cycles, weighted by the distance covered in each part.