Fiat has been named as the top car manufacturer with regards to CO2 emissions by CleanGreenCars.co.uk.
A study by the site calculated the average CO2 emissions of vehicles made by major car manufacturers across the world and found that the typical Fiat car was responsible for releasing 141 grams of carbon dioxide per kilometre in the first quarter of 2007.
Next in the list were Peugeot, Citroen, Toyota and Skoda, with emissions ranging from 148g/km to 153g/km.
Jay Nagley, publisher of CleanGreenCars.co.uk, commented: "People can assume that manufacturers of hybrid cars must be the best, but the truth is more complex. Making lots of efficient modern diesels actually has a bigger impact on CO2 performance than making a few hybrids.
"The top three marques are all pioneers of modern diesel engines while Toyota, although much better than average, is not absolutely the best."
When the study was restricted to the UK, the top companies were found to be Ford (155g/km), Vauxhall (157g/km) and Volkswagen (158g/km).
Special mention was also given to Mini as the most improved automaker, with a 13 per cent reduction in its emissions levels between the first quarters of 2006 and this year.