Emissions of CO2 and other greenhouse gases are responsible for climate changes. The replacement of gasoline passenger cars by Diesel ones, which emit less CO2, can be an efficient way to decrease CO2 emissions. This replacement can be more effective in countries with low Diesel penetration. Norway belongs to the above countries, and although a significant increase in the sales of Diesel passenger cars has been observed during the last years, the overall Diesel penetration remains lower than 23%. Several scenarios, using the current and estimated future passenger car sales and fuel consumption, are used to study the benefit in CO2 emitted from new passenger cars in this country. The results show that a CO2 benefit of more than 1.6% can be achieved, if a Diesel penetration would reach levels up to 30% on the basis of the current fleet; this advantage could be even 6.1% if the Diesel penetration would reach levels up to 50%. While increasing Diesel penetration and reducing vehicle weight are efficient ways to control CO2 emissions from the transport sector, future fuel consumption of gasoline and Diesel passenger cars would also play a key role in this direction.