Sediment analysis using wet extraction techniques and model simulations were carried out to investigate the role of ferric iron during biodegradation of dissolved petroleum hydrocarbon compounds at a field site in Perth, Western Australia. Sediment cores were analysed for iron and sulphur species. The total iron concentrations were found to be low while the fraction of Fe(II) was surprisingly high. Pyrite was detected in the contaminated zone, but no iron monosulphides were found. A reactive multi-component transport model, coupling advective- dispersive transport of organic compounds and inorganic aqueous components with a geochemical equilibrium model and a biodegradation module, was applied to simulate qualitatively the fluxes and reactions involved in the biodegradation of BTEX compounds. Both field investigations and modelling suggest that ferric iron minerals play no important role as electron accepters while sulphate provides the major part of the oxidation capacity.