This paper analyses what post 2020 targets may be necessary for the European CO2 legislation for passenger cars in order to reach the overall sectoral goal of 60% reduction of transport's greenhouse gas emissions by 2050 relative to 1990, as defined in the European Commission's White Paper. The required target levels are found to depend strongly on the contribution that passenger cars need to make to reaching the overall target, on the assumed growth of passenger car mobility, and on the extent to which biofuels could be available for fuelling passenger cars. To what extent electric vehicles and other low emission vehicles such as plug-in hybrids and fuel cell electric vehicles are needed to meet the post-2020 targets depends on the target level and on the minimum CO2 emissions that can be reached in conventional vehicles. Almost all assessed scenarios, require significant amounts of low emission vehicles to be sold from 2030 or 2035 onwards. Electric and plug-in vehicles are in the early stage of market introduction now, but developments are fragile could end up in a 'valley of death'. Defining a sufficiently low passenger car CO2 target for 2025 may be an effective instrument to motivate manufacturers to continue their efforts in the marketing and further development of these vehicles. This is important for maintaining the momentum of the transition towards large-scale application of low CO2 emitting vehicles.