A process for the vapor phase ammoxidation of alkanes and olefins with a catalyst of the general empirical formula: VSbaMbQcOx wherein M is at least one element selected from magnesium, aluminum, zirconium, silicon, hafnium, titanium and niobium, Q is at least one element selected from rhenium, tungsten, molybdenum, tantalum, manganese, phosphorus, cerium, tin, boron, scandium, bismuth, gallium, indium, iron, chromium, lanthanum, yttrium, zinc, cobalt, nickel, cadmium, copper, strontium, barium, calcium, silver, potassium, sodium and cesium, a is 0.5 to 20, b is 2 to 50, c is 0 to 10 and x is determined by the valence requirements of the elements present. The process has a co-feed of gaseous carbon dioxide with an alkane (paraffin) and/or alkene, ammonia and an oxygen-containing gas which react in the presence of the catalyst to form a nitrile and by-products.