This article presents the results of a pilot-scale evaluation of an advanced oxidation process that utilizes hydrogen peroxide and ozone. Treatment efficiency was determined as a function of the hydrogen peroxide-to-ozone dosage ratio, ozone dosage, and contact time. The ozone mass transfer characteristics of the process were also investigated. Comparison with other treatment technologies indicates that advanced oxidation can be a cost-effective treatment process for controlling the common chlorinated organics found in groundwater. Includes 23 references, tables, figures.