An apparatus for performing continuous flow chemical reactions such as oxidation, oxidative dehydrogenation and partial oxidation processes involving a reactor design characterized by controlled/optimized addition of a reactant with the objective of: (i) avoiding the explosion regime of the reactant mixture (e.g., hydrocarbon/oxidant mixture); (ii) maximizing the selectivity of the reaction to the desired product; (iii) limiting the reactor temperature gradient and therefore the threat of reaction runaway; and (iv) controlling the operating temperature of the reaction zone so that desirable temperature range is maintained over the entire zone.