The best improvement figures came from the Mini (which turned in CO2 numbers that are 17.32 percent better), followed by Jeep (10.83 percent), BMW (6.48 percent), Mitsubishi (6.29 percent) and Land Rover (4.10 percent). Note that this is just measuring improvement. The top five marques with the lowest CO2 emissions in 2007 were Fiat (142.15 g/km), Peugeot (146.04) , Daihatsu (146.9), Mini (147.26) and Citroën (148.07).
The model with the least CO2 emissions was the Toyota Prius (104 g/km), followed by the Toyota Aygo/Peugeot 104/Citroën C1 triplets (109) and the Smart Fortwo (116.39). Note, as well, that it's the average figures for a specific model and all versions were considered. CO2 figures are relevant for British motorists because their road tax is calculated depending on these figures.