This paper studies the determinants of fuel use in the trucking industry in Denmark, using aggregate time series data for the period 1980–2007. The model captures the main linkages between the demand for freight transport, the characteristics of the vehicle fleet, and the demand for fuel. Results include the following. First, we precisely define and estimate are bound effect of improvements in fuel efficiency in the trucking industry:behavioural adjustments in the industry imply that an exogenous improvement in fuel efficiency reduces fuel use less than proportionately. Our best estimate of this effect is approximately 10% in the short run and 17% in the long run, so that a 1% improvement in fuel efficiency reduces fuel use by 0.90% (short-run) to 0.83% (long-run). Second, we find that higher fuel prices raise the average capacity of trucks, and they induce firm sto invest in newer, typically more fuel efficient, trucks. Third, these adjustments and the rebound effect jointly imply that the effect of higher fuel prices on fuel use in the trucking industry is fairly small; estimated price elasticities are _0:13 and _0:22 in the short run and in the long run, respectively. The empirical results of this paper have implications for judging the implications of fuel efficiency standards and regulations with respect to larger trucks in the EU.