The primary problem regarding the introduction of new energy sources is whether they will alter the mutagenicity, carcinogenicity and potential human cancer risk from combustion emissions. New risk assessment methodologies utilizing data from short-term bioassays, therefore, are needed to assess new technologies as they are being developed. This will allow the development of alternative combustion and control methods that lower human risk. In order to assess the relative human cancer risk associated with introducing diesel-powered automobiles as an alternative fuel-efficient energy source for transportation, the authors have developed a comparative data base and risk assessment methodology. This risk assessment model and methodology is applicable to the evaluation of various complex mixtures. The paper describes a comparative approach to evaluating alternative energy sources by utilizing short-term genetic bioassays.