Even if current engines consume less fuel than they used to, the thermal efficiency of an internal combustion engine has not really increased since its creation. The peak efficiency reached by a 4-cycle Otto cycle engine is around 35%, which means that 65% of the energy contained in the fuel is lost as pumping losses, friction losses, cooling losses, exhaust losses and accessories. High speed Diesel cycle engines fare better with around 45% peak efficiency, but are still far from their Carnot efficiency, and hence 55% of the fuel energy content is lost.