Mobile bacterial particles can act as carriers and enhance the transport of hydrophobic contaminants in groundwater by reducing retardation effects. Because of their colloidal size and favorable surface conditions, bacteria act as efficient contaminant carriers. When such carriers exist in a water-saturated porous medium, the system can be thought of as three phases: an aqueous phase, a carrier phase, and a stationary solid matrix phase. Contaminant may be present in either or all of these phases. In this study, a mathematical model based on mass balances is developed to describe the simultaneous transport and fate of a biodegradable contaminant and bacteria in a porous medium. The Monod model describes the relation between the growth rate of bacteria and concentration of the contaminant which serves as a growth substrate. The bacterial decay is assumed to be a first-order reaction. The mechanisms of bacterial mass transfer between aqueous and solid matrix phases, and contaminant mass transfer between aqueous and bacterial phases are represented by kinetic models. Governing equations are nondimensionalized and solved to analyze the bacteria-facilitated contaminant transport. The model is compared with a similar model obtained with local equilibrium assumption to understand the characteristics of kinetic and local equilibrium descriptions. Results show that the contaminant transport as well as bacterial transport can be described by local equilibrium assumption when Damk¿hler numbers are larger than 10. Significant sensitivities to model parameters, particularly bacterial growth rate and influent bacterial concentration, were observed. The numerical results of the bacteria carrier effect match favorably with experimental data reported in the literature. ¿ American Geophysical Union 1996