Largely as a result of the rapid wartime development of gas turbines for aircraft usage, renewed emphasis has been placed upon the development of gas turbines for industrial applications. At the present time a number of domestic organizations are quite active in this field. One of the principal industrial applications of gas turbines in the United States is their use in the Houdry catalytic-cracking process in the oil-refining industry. Recent development work is centered around their use in the field of locomotive and marine propulsion using either coal or oil as fuel. The ultimate choice of a fuel is a complex problem involving such factors as fuel cost, engine performance and maintenance, and fuel availability. As far as fuel oils are concerned, the designer is further confronted with a wide variety of grades from which to choose. This paper presents information on the fuel properties and characteristics which are commonly employed for the identification and specification of such fuel oils, and also on those properties which are felt to be of significance with regard to fuel-system design and combustion-chamber and gas-turbine performance. Since fuel cost and availability are intimately related to supply and demand considerations, only limited regard is given to these factors in the present paper.