The contribution of direct (molecular ozone) and indirect (HO radical) oxidation of bromide to bromate has been investigated during batch ozonation of model solutions. "Pure" natural organic matter (NOM) has been isolated by XAD-8 resin adsorption (humic substances). The direct oxidation pathway was separated from the indirect oxidation pathway through the use of a radical scavenger (t-butanol). Although inorganic carbon sufficiently scavenged HO radicals, it was observed to behave as a secondary oxidant and increased the amount of bromate formed upon ozonation. Indirect oxidation of bromide species contributed to approximately 75% of the total bromate formed in NOM-free (Milli-Q) water, and ranged from 70% to greater than 95% in the presence of NOM. The relative contribution of the indirect oxidation pathway increased as a function of pH. Bromate control strategies such as ammonia addition or pH depression may be affecting the indirect oxidation (HO radical) pathway in addition to the direct (molecular ozone) oxidation pathway which is dependent upon the hypobromite ion (OBr) concentration.