This paper estimates the trends of fleet car fuel efficiency and new car fuel efficiency in Great Britain and analyses determining factors of the changes in car fuel efficiency. According to the analysis results, the pure technology effect was partly offset by the increase of average engine capacity of vehicles, especially since the late 1980s. Although in the 1990s, the pure technology effect itself was much reduced than in the earlier period, the shift in consumer choice to bigger cars also obstructed the improvement of fuel efficiency in this period. Meanwhile, this study found about a 10% gap between the official fuel consumption rate of new cars and on road fuel consumption rate, which generally confirms the result of earlier studies. (c) 2005 Elsevier Ltd. All rights reserved.