This paper estimates firm level energy efficiency and its determinants in 14 sectors of Swedish manufacturing by using stochastic frontier analysis (SFA). We derive energy demand frontiers both from cost minimizing and profit maximizing perspectives. To account for firms’ heterogeneity, Greene’s true random effects model is adopted. Results show that, from both firm behavior perspectives, there is room to improve energy efficiency in all sectors of Swedish manufacturing. The EU ETS seem to have had a moderate or no effect on Swedish firms’ efficient use of energy. Moreover, we found that energy intensity or energy productivity (energy use over production value) is not an appropriate proxy for energy efficiency.