The 2020 Sustainable and Smart Mobility Strategy explicitly includes the provision of better information on the greenhouse gas (GHG) performance of individual transport operations as a key instrument to incentivise transport users and operators to lower the GHG impact of their transport decisions. The information has the potential to empower transport users to compare transport modes and operators on their GHG emissions performance. Furthermore, the information might also be used to create a system of credentials for operators, which could then find its way into contractual agreements and procurement processes, but also, for example, into green financing mechanisms or the development of consumer labelling schemes. In the current ecosystem of transport GHG emissions accounting, different methodologies and data from different sources and of different quality are used by a diversity of organisations. These differences make comparison of GHG emissions figures from transport services complicated and hence hamper the use of this type of information by both transport users and operators. The European Commission has recognised this problem, and it therefore announced the CountEmissions EU initiative, with the aim to establish an EU framework for harmonised accounting of transport and logistics GHG emissions. The objective of the support study is to provide the Commission with robust evidence on the problem logic, policy options and potential impacts of CountEmissions EU. Based on the evidence collected and the further analysis, a preferred option for the implementation of the initiative on the EU internal market has been identified.