ABSTRACT: An "oxygen barrier" was formed by depositing an oxygen-releasing compound in a series of wells that were placed perpendicular to the direction of groundwater flow at a site in Belen, New Mexico. The objective was to enhance the intrinsic bioremediation of dissolved phase BTEX contamination in the aquifer and to quantify the results. The oxygen was supplied by a controlled release formulation of magnesium peroxide called Oxygen Release Compound (ORC®), a virtually insoluble powder that is packaged in polyester filter socks. The areal distributions of the initial concentrations of dissolved oxygen and BTEX were measured and compared to the concentration changes at various times in the first 93 days of system operation. The concomitant reduction in BTEX can be seen in a series of contour plots. In 93 days, dissolved oxygen had dispersed at least 20 feet downgradient from the ORC source wells based on the pattern of decreasing BTEX concentrations.