This paper presents a study that was conducted to investigate the impact and significance of oxidation of ozone and peroxone (ozone combined with hydrogen peroxide) for methyl tertiary-butyl ether (MTBE) removal from the City of Santa Monica's groundwater. Experiments conducted in a semi-batch reactor demonstrate that Peroxone was consistently effective in oxidizing MTBE than was ozone alone. However, applied ozone doses greater than 10 mg/L are necessary for both spiked MTBE concentrations at approximately 200 and 2,000 ug/L to achieve MTBE levels below the California drinking water secondary standard of 5 ug/L. Both ozone and peroxone can degrade MTBE into biodegradable products such as t-butyl formate, t-butyl alcohol, acetone, and aldehydes. In addition, peroxone can oxidize MTBE more rapidly than ozone alone. When peroxone was used, the formation of bromate ranged from "not detected" to 13 ug/L exceeded the maximum contaminant level of 10 ug/L. It appeared that bromate formation can be effectively controlled with hydrogen peroxide-to-ozone ratios greater than 1.0.