During oxidative treatment of water with chlorine or ozone, the bromide present is oxidized to hypobromite. Oxidation to bromate, though thermodynamically possible, occurs with very low rates. Attemps were made to distinguish by experiment between the role of chlorine in oxidation reactions and in substitution reactions. When chlorine and bromine react in combination, it appears that chlorine preferentially acts as an oxidant while bromine reacts more as a halogenating agent. Analogous behavior was observed when ozone is combined with halogens.