For the purpose of developing an automobile which keeps low pollution using petroleum substituting clean energy, decreases the running energy consumption to a half at least, and reduces the CO2 emission to less than a half of the conventional one at the same time, the R and D started in fiscal 1997. As to the study of a high efficiency hybrid power system, conducted were the prediction of fuel consumption performance of the system proposed, evaluation of element technology using hybrid simulator, evaluation experiment on a new hybrid vehicle, and grasp of overseas trends. In relation to the development of hybrid vehicles, the following were studied: methanol fuel cell loading hybrid vehicle, CNG engine loading hybrid vehicle, CNG ceramic engine loading hybrid truck, CNG lean burn engine loading hybrid truck, LNG engine loading hybrid bus, and DME engine loading hybrid bus. Besides, a survey on synthetic fuel and the related survey were carried out. 17 refs., 185 figs., 101 tabs.