Going over old ground for sure, but I'm interested in a few specific answers. If you assume the standard measurement of fuel economy is accurate in test conditions as well as road conditions (?) then...... 1. Why are drivers of large diesel engined cars not achieving these figures? 2. Can buyers of new cars return the car under the sale of goods act for the above? 3. Is this a phenomena specific to large diesel engines? ie. high power to engine capacity ratio 4. Are all OEMs the same or are some cars easier to achieve claimed mpg figures? If so, why? I suspect the answer of (1) to be diverse. My personal view is that the test does not reflect modern motoring and certainly not how most people drive their cars. I also suspect the car to have been optimised for this test and for efficiency to quickly drop off if the parameters are exceeded. 2. I would guess at, yes 3. Is this owners simply using the power more than the efficiently capability of their car. 4. I've found cars with cruise control easier to achieve good mpg than those without. Simply because it stops me following the speed of the car in front when on a motorway. With cruise I bumble along at 60mph, overtake a few hgv and have many cars overtake me, allowing me to simply do my own thing. I accept this will not be the same for everyone. Having just bought a largish engined (3.0 V6) diesel for the first time myself I'm quite happy with my overall efficiency of 44mpg. So I'm curious to know why owners of more modern engines are less happy and what old car should I be buying in 5-10 years time if the current crop is allegedly so poor?