Control of CO2 emissions is a major environmental issue in most countries. The Swedish car market shows remarkably low new Diesel passenger car registrations compared to the average European Union car market. Therefore, a simple way to decrease CO2 emissions from the transport sector in Sweden would be the replacement of gasoline by Diesel passenger cars, which emit less CO2. The combined effects of probable changes in Diesel and gasoline future fuel consumption, new passenger car sales and market segmentation have been evaluated for different Diesel passenger cars penetrations. The results show a benefit in CO2 emissions of about 2.8% with 30% Diesel penetration; if Diesel penetration reaches 50%, the benefit attains 7.5%. Future rises of CO2 emissions caused by higher new passenger car registrations or unfavourable market segmentation could be at least partially counterbalanced by the introduction of more Diesel passenger cars. Copyright (c) 2006 John Wiley & Sons, Ltd.