A process for the ammoxidation of a saturated or unsaturated or mixture of saturated and unsaturated hydrocarbon to produce an unsaturated nitrile, said process comprising contacting the saturated or unsaturated or mixture of saturated and unsaturated hydrocarbon with ammonia and an oxygen-containing gas in the presence of a catalyst composition comprising molybdenum, vanadium, antimony, niobium, tellurium, optionally at least one element select from the group consisting of titanium, tin, germanium, zirconium, hafnium, and optionally at least one lanthanide selected from the group consisting of lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium. Such catalyst compositions are effective for the gas-phase conversion of propane to acrylonitrile and isobutane to methacrylonitrile (via ammoxidation).