In the present study, exergy and pinch analyses have been performed on ammonia-water and Rankine bottoming cycles for gas diesel engines. Gas diesel engines produce four waste heat streams at different temperature levels that can be used as heat sources by a bottoming cycle. The ammonia-water cycle has the potential to use these heat sources more efficiently than a Rankine cycle. The second law efficiency of the best ammonia-water cycle configuration is 43-48 % higher than the efficiency of a single-pressure Rankine cycle and 20-25 % higher than the efficiency of a dual-pressure Rankine cycle. This paper was presented at the ECOS’00 Conference in Enschede, July 5-7, 2000