The invention relates to a process of the oxidative dehydrogenation of an alkane containing 2 to 6 carbon atoms and/or the oxidation of an alkene containing 2 to 6 carbon atoms, wherein a gas stream comprising oxygen and the alkane and/or alkene is contacted with a mixed metal oxide catalyst containing molybdenum, vanadium, niobium and optionally tellurium, and wherein the linear velocity of said gas stream is at least 10 cm/sec.