Because of high oil prices, and climate change policy, governments are now seeking ways to improve new car fuel economy thus contributing to air quality and energy security. One strategy is to increase dieselisation rates of the vehicle fleet. Recent trends in fuel economy show improvement since 1995, however, efforts need to go further if the EU Voluntary Agreement targets on CO2 (a greenhouse gas emission standard) are to be achieved. Trends show diesel car sales have accelerated rapidly and that the advantage of new car fuel economy of diesel cars over gasoline ones is narrowing posing a new challenge. We estimate the demand for new car fuel economy in the UK. In the long-run consumers buy fuel economy, but not in the short-run. We found that long-term income and price changes were the main drivers to achieve improvements particularly for diesel cars and that there is no break in the trend of fuel economy induced by the agreement adopted in the 1990s. Policy should target more closely both consumer choice of, and use of, diesel cars. (C) 2009 Elsevier Ltd. All rights reserved.