The energy crisis of recent years is primarily a petroleum shortage. Thus because the depletion of world petroleum reserves can now be foreseen, a new form of portable energy will be needed to power gasoline and diesel engines. Alcohol is a portable, clean-burning form of energy that is already in limited use as a partial replacement for gasoline and diesel. The state of the art of gasohol （a blend containing, by volume, 10∼20 % anhydrous alcohol and 80∼90 % gasoline） and diesohol (a blend containing, by volume, 10 % or more anhydrous alcohol and 90 % or less diesel fuel) as conventional engine fuels is reviewed in two parts, the former in Part(I) and the letter in Part(II). Physico-chemical properties and performance characteristics of the blended fuels are discussed in conjunction with conventional engines. Alcohol-diesel blends exhibit, from one stand point, near interchangeability with, and from a different stand point, better performance characteristics than neat diesel fuels if some hardware modifications can be made. Necessity of product-oriented development work was stressed in order to arrive at "Engineered Fuel Formulations" encompassing as many different designs of engines and fuel compositions as possible. Also, economics aspects including that of producing ethyl alcohol from biomass are discussed.