The price differential between distillate and residual fuels tends to increase rather than decrease, offering a growing incentive to the use of residuals in diesel engines. In general, no specifications can be put upon residuals without largely eliminating the price advantage. Therefore special measures must be taken to assure trouble-free operation on residual fuels. Significant strides have been made in this direction, especially with regard to lubricants. New developments in protective lubrication, engine tests, and service results are discussed.