Although i dont disagree that some people will be getting 40-50mpg from their Prius, i do also trust independant studies that realise the result closer to what i originally stated (there are some quite in-depth ones relating to prius vs other small eco cars regarding fuel/c02). But in all honesty if you are mostly concerned with MPG over c02, then you will get plenty of diesels that arent small (rollerskates), slow but are reliable and capable of running over 40mpg. I own a 1.9tdi Skoda Fabia VRS, its tuned for brisk driving, has proper poke in the upper gears due to massive torque. My car computer says average fuel consumption at 42mpg at the moment, and its never driven with over caution. On long journeys its easy to sit at about 55mpg. I would guess some decent 1.9tdi's from VW group, that arent in such a high state of tune would give a regular 50mpg and arent in the small rollerskate group of cars.