Bromate formation in conventional ozonation and advanced oxidation processes combining ozone and hydrogen peroxide was investigated at five water treatment plants. Before ozonation, bromide concentrations ranged from 35 to 130 mu g/L. Bromate formed during the ozonation step varied from <2 to 42 mu g/L. In general, advanced oxidation leads to higher bromate concentrations when compared with a conventional ozonation process, if the same ozone residual is maintained for both processes. Lower concentrations result if the ozone dosage is kept constant and the hydrogen peroxide dosage is increased.