This report summarises the analysis done on the data provided to the European Commissions’ Joint Research Centre by the Heavy Duty Vehicle manufacturers about the 2016 Heavy Duty Vehicles’ fleet composition and CO2 emissions performance. The results comprise of key metrics and a representative fleet-wide CO2 emissions baseline distribution for the year 2016 which were key inputs to the impact assessment study that supported the European Commission's proposal for new Heavy-Duty Vehicle CO2 standards in Europe. All datasets were checked for quality and errors and were validated against similar data calculated by external parties. CO2 emissions values were normalised to a common reference basis and CO2 distributions were produced for the four vehicle categories of interest. The normalisation process led to lower fleet-wide CO2 emissions, an important observation for defining realistic CO2 limits for the post-2020 period.