The IEB research program in Infrastructure and Transport promotes high quality research in those fields in order to assess the economic consequences of investment and policy decisions. The ultimate aim of the program is to generate socially useful knowledge in this important field that is useful to respond to major challenges. Research is methodologically based on the techniques of applied economic analysis, with topics chosen according to their relevance in guiding public policy. Infrastructures and transport policies are closely related with economic growth, public finance, environmental issues and distribution effects at a territorial level. Disseminating research outputs to a broadaudience is an important objective of the program, whose results must be relevant both at national and international level.The Barcelona Institute of Economics (IEB) is a research centre at the University of Barcelona (UB) which specializes in the field of applied economics. The IEB is a foundation funded by the following institutions: Applus, Abertis, Ajuntament de Barcelona, Diputació de Barcelona, Gas Natural, La Caixa and Universitat de Barcelona. The IEB working papers represent ongoing research that is circulated to encourage discussion and has not undergone a peer review process. Any opinions expressed here are those of the author(s) and not those of IEB. This paper estimates the role that technological change and car characteristics have played in the rate of fuel consumption of vehicles over time. Using data from the Spanish car market from 1988 to 2013, we estimate a reduced form equation that relates fuel consumption with a set of car characteristics. The results for the sales-weighted sample of vehicles show that energy efficiency would have improved by 32% and 40% for petrol and diesel cars respectively had car characteristics been held constant at 1988 values. However, the shift to bigger and more fuel-consuming cars reduced the gains from technological progress. Additionally, using the results of the fuel equation we show that, besides a natural growth rate of 1.1%, technological progress is affected by both the international price of oil and the adoption of mandatory emission standards. Moreover, according to our estimations, a 1% growth in GDP would modify car characteristics in such a way that fuel consumption would increase by around 0.23% for petrol cars and 0.35% for diesel cars.JEL Codes: L62, Q50, R4