European traffic volumes have grown substantially in recent years, leading to greater emissions of an array of pollutants, including the greenhouse gas CO2. At the request of the Swedish Environmental Protection Agency (EPA), CE Delft has carried out an exploratory study to assess the potential, and the pros and cons, of a system of tradable CO2 emission rights for the transport sector. Europe already has an emission trading system (ETS) for energy-intensive industry. Alternative forms of an emission trading system were analysed (cap & trade versus baseline & credit, upstream versus downstream), as well as systems for the entire transport sector versus individual systems for road, rail, aviation, shipping and so on. It was also examined whether it would make more sense to have a separate emission trading system for transport, or one linked to the current European ETS. The variant schemes were then evaluated on a number of yardsticks, including environmental impact, cost effectiveness and effect on the competitive position of the respective sectors.