The combustion characteristics of hydrogen compared to gasoline offer the potential of an
increased engine efficiency, especially at part load. Here, results are presented of the brake thermal efficiency of a bi-fuel hydrogen/gasoline engine, at several engine speeds and loads. Results on hydrogen are compared to results on gasoline. Hydrogen offers the possibility of a more flexible load control strategy. Where possible, results are compared between the wide open throttle, lean burn strategy and the throttled stoichiometric strategy.