A diesel fuel containing a soot dispersant additive which is a grafted and derivatized low molecular weight copolymer of ethylene and at least one C3-C10 alpha monoolefin is provided. Also provided is a method for improving the fuel economy of a diesel engine which comprises operating the diesel engine with a fuel composition comprising (a) a major amount of a diesel fuel and (b) a minor fuel economy improving effective amount of the soot dispersant additive.