Catalysts comprising a carbon-containing sulfide of molybdenum or tungsten are prepared by contacting, in the presence of sulfur, hydrogen and a hydrocarbon, ammonia and ammonium substituted molybdate, thiomolybdate, tungstate and thiotungstate salts at a temperature of from about 200.degree.-600.degree. C. These catalysts are useful for hydrotreating reactions. In a preferred embodiment, these catalysts will be promoted with certain transition metal sulfides, such as cobalt sulfide, which results in catalysts having greater activity than conventional catalysts such as cobalt-molybdate on alumina.