The subject of this study is the trade-off between fuel economy and transient performance in turbocharged engines. It quantifies the losses and gains of different engine control strategies. Two extreme strategies are analyzed, one for optimal fuel economy and the other for fast transient response. Models for the components that influence the fuel economy are developed and described. An optimization problem for best fuel economy is solved analytically and a fuel-optimal controller is implemented based on that result. This controller is compared to one which is optimized for fast transient response with respect to the gains in fuel economy and losses in transient response. Simulations of a highly boosted engine show that a fuel-optimal controller can improve the fuel economy of a vehicle operated at cruising speed by 1-3% and at highway speed by 4%, and that the highest achievable improvement is above 10%. The losses in transient response are around 0.4 s for cruising conditions. Furthermore, measurements on a low-boosted engine on a test bench are used to show that the fuel-optimal controller reduces fuel consumption by 1.9% at highway conditions.