Abstract The author gives examples of the various specification requirements encountered by the oil refiners, and points out the impossibility of carrying several grades of Diesel fuel oil at distributing points which are not also refining centers. Unless Diesel engines are constructed which can operate efficiently on a standard grade of oil of broad specification, ship operators will be unduly restricted to limited points of fuel supply and may be precluded from operating in the most desirable trade services. He suggests that three specifications would be sufficient: a minimum gravity of 24 deg. A.P.I., a maximum sulphur content of 1.5 per cent, and a minimum flash of 150 deg., closed cup.