Two column tests were conducted using aquifer material to simulate the nitrate field demonstration project carried out earlier at Traverse City, Michigan. The objectives were to better define the effect nitrate addition had on biodegradation of benzene, toluene, ethylbenzene, xylenes, and trimethylbenzenes (BTEX) in the field study, and to determine whether BTEX removal can be enhanced by supplying a limited amount of oxygen as a supplemental electron acceptor. Columns were operated using limited oxygen, limited oxygen plus nitrate, and nitrate alone. In the first column study, benzene was generally recalcitrant compared to the alkylbenzenes (TEX), although some removal did occur. The average benzene breakthroughs were 74.3 + or - 5.8%, 75.9 + or - 12.1%, and 63.1 + or - 9.6% in the columns with limited oxygen, limited oxygen plus nitrate, and nitrate alone, respectively, whereas the corresponding average effluent TEX breakthroughs were 22.9 + or - 2.3%, 2.9 + or - 1.1%, and 4.3 + or - 3.3%. In the second column study, nitrate was deleted from the feed to the column originally receiving nitrate alone and added to the feed of the column originally receiving limited oxygen alone. Benzene breakthrough was similar for each column. Breakthrough of TEX decreased by an order of magnitude once nitrate was added to the microaerophilic column, whereas TEX breakthrough increased by 50-fold once nitrate as removed from the denitrifying column. Although the requirement for nitrate for optimum TEX removal was clearly demonstrated in these columns, there were significant contributions by biotic and abiotic processes other than denitrification which could not be quantified.