Abstract An efficient way to decrease the CO2 emissions is the replacement of gasoline passenger cars (PC) by diesel ones, which emit less CO2. This can be more effective in Greece where the percentage of new diesel PC remains less than 1%, contrary to the other countries of the European Union, which have high diesel penetrations. The benefit of CO2 emitted from new PC is studied in the case of an increased percentage of diesel PC in Greece, using several scenarios taking into account the current and future new car registrations and fuel consumption. The results show that a CO2 emission reduction of more than 5.2% can be achieved if a diesel penetration higher than 30% occurs in the case of current fleet. If the penetration reaches 50%, this benefit is higher than 10.5%. Exhaust CO2 emissions from future new PC will increase significantly in this country and can be partially controlled by the introduction of diesel PC.