A method for controlling the deposits in the fuel vaporizer of a fuel reformer used to prepare a liquid hydrocarbon for use as a fuel in a fuel cell which comprises introducing into the fuel vaporizer a liquid hydrocarbon containing an effective deposit controlling amount of a nitrogen-containing detergent additive and a fuel composition suitable for use in a fuel cell which comprises a liquid hydrocarbon having a boiling range at atmospheric pressure falling between about 77 degrees F. (25 degrees C.) and about 437 degrees F. (225 degrees C.), a total sulfur content of less than 3 ppm, and containing an effective deposit controlling amount of a nitrogen-containing detergent additive.