This study compares official fuel consumption values measured in laboratories with the real-world performance of 20 popular vehicle models. All models claim significant improvements in fuel efficiency since 2009, with reductions in official fuel consumption values ranging from 8 to 30 percent. On-road measurements, however, indicate that eight models made little to no improvement in
real-world fuel efficiency. Five models achieved more than a 10 percent reduction in real-world fuel consumption since 2009. Model overhauls are frequently followed by abrupt reductions in official fuel consumption values. Real-world fuel consumption values are, however, rarely reduced to the same extent, indicating that fuel efficiency improvements measured during laboratory testing do not fully materialize on the road.