This report describes how the gap between official vehicle carbon dioxide emissions and real-world carbon dioxide emissions continues to grow in the European Union, from 8 per cent in 2001 to 38 per cent in 2014. For an average consumer, this translates to additional fuel expenses because vehicle-taxation schemes and incentive schemes for low-carbon cars are based on official carbon dioxide values. This could also lead to significant losses of tax revenue and misallocation of public funds. The report outlines several reasons for the increasing gap and identifies the implications.