Dissimilatory iron-reducing bacteria derive energy needed for growth and function by oxidation of organic compounds or molecular hydrogen coupled with reduction of iron(III) to iron(II) in subsurface environments. In this work, we used the indicated bacteria in an anaerobic environment for oxidation of benzene, toluene, ethylbenzene, and xylenes (a mixture of o-, m-, and p-xylenes) (BETX), which are aquifer contaminants. We show that oxidation of aromatic hydrocarbons coupled with bacterial reduction of iron follows first-order kinetics. The rate constant is maximum for an aromatic hydrocarbon:Fe ratio equal to 1. The oxidation rate constant increases in the series benzene < toluene < ethylbenzene < xylenes. The aromatic hydrocarbon degradation efficiency increases as the concentration of the substrate (citric acid) increases.