Formation of bromate is of a great concern whenever ozone-based technologies are used for treating highly bromide-containing water ever since bromate was classified as a potential carcinogen. Saudi Arabian groundwater is coincidentally high in bromide content, and the potential of forming bromate during the treatment of such water is high. This study investigated the extent of bromate formation under different treatment conditions of ozone-based Advanced Oxidation Processes (AOPs) when used for the treatment of phenol-contaminated water. The results of the study showed that continuous ozonation at a rate of 1 L/min has completely removed 50 ppm of phenol from contaminated water in less than 5 min. However, as high as 8.85 ppm of bromate (BrO3-) was detected when treating the water which has high concentration of bromide ion (5 ppm). Results also showed that by adjusting the pH to 6 and adding ammonia (NH3) at a dosage of 1.5 ppm, bromate formation was diminished drastically to non-detected levels. (C) 2010 Elsevier B.V. All rights reserved.