Degradation of benzene, toluene, and ethylbenzene (BTE) by microbial populations indigenous to the soil and populations proliferated from the indigenous using biogenic substrates were compared. The reaction system consisted of aerobic microcosms representing an unsaturated soil. Microcosms supplemented with glucose and citrate, when compared to the unsupplemented microcosms, showed increases in bacterial counts, but the overall degradation rates for B, T, or E were reduced in spite of shorter lag times. Both biogenic substrate supplements were non-beneficial for BTE degradation due largely to the preferential and healthy growth of the indigenous populations on the biogenic substrates, and thus the urgency of developing a favorable amount of BTE degraders was reduced.