A model to describe the biodegradation of benzene, toluene, ethylbenzene and o-xylene (BTEX) and growth of a bacterial consortium was systematically developed from a series of aerobic batch degradation experiments. The bacterial consortium was enriched from petroleum contaminated soil on a mixture of BTEX components and was identified to contain 7 unique species of Pseudomonas. Parameter estimates are reported for both conventional Monod parameters obtained from single substrate degradation experiments and interaction parameters obtained from dual substrate experiments. Key interactions identified include both the inhibition and enhancement of biodegradation rates for mixed substrates relative to single substrate experiments. Enhancement interactions have been qualitatively observed by other authors to occur to BTEX mixtures, but have not been quantified previous to the current study. Observations include the inhibition of benzene degradation in the presence of toluene and in the presence of ethylbenzene. As well, enhanced degradation of benzene was observed in the presence of o-xylene and toluene degradation was enhanced in the presence of benzene. A sum kinetics with interaction parameters (SKIP) model was found to accurately describe these interactions. In addition, it was found that o-xylene was cometabolized in the presence of toluene and/or benzene and a mathematical model was used to describe this interaction. The SKIP and cometabolism models were combined to predict both BTEX degradation as well as biomass production for this consortium when all BTEX components are present simultaneously. (C) 2008 Elsevier Ltd. All rights reserved.