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Two methods were used to approximate site‐specific biodegradation rates of monoaromatic hydrocarbons (benzene, toluene, ethylbenzene, and xylenes [BTEX]) dissolved in ground water. Both use data from monitoring wells and the hydrologic properties of the quifer to estimate a biodegradation rate constant that can be used in ground water solute fate and transport models. The first method uses a biologically recalcitrant tracer in the ground water associated with the hydrocarbon plume to normalize changes in concentration of BTEX under anaerobic conditions; attenuation of the tracer is attributed to dilution, sorption, and/or volatilization. Attenuation of BTEX in excess of the attenuation of the tracer is attributed to biodegradation, although other processes may affect the observed rate. The second method assumes that the plume has evolved to a dynamic steady‐state equilibrium. A one‐dimensional analytical solution to the advection‐dispersion equation is used to extract the rate of attenuation that would be necessary to produce a steady‐state plume of the configuration found at the site. Attention is attributed largely to biodegradation bacause the analytical solution removes the effects of sorption and dispersion and volatilization is assumed to be minimal. Neither method fully accounts for the effects of continuing dissolution of BTEX in the source area or nonlinear sorption. Therefore, the rats cannot be attributed fully to biodegradation, but still are useful for ground water contaminant fate and transport modeling. The methods were applied to a data set from a JP‐4 jet fuel spill at Hill Air Force Base, Utah. In estimats along two seprate flow paths, natural attenuation rates for BTEX ranged form 0.006 to 0.038 day−1, with most rates near 0.02 day−1. The rate for benzene ranged from 0.025 to 0.038 day−1. The rates of attenuation of individual BTEX compounds as estimated by the two methods were in close aggrement. For an individual compound, the rate estimated using the second method was at most 36 percent greater than, but usually within 20 percent of, the rate estimated using the first method, suggesting that intrinsic bioremediation was the dominant process that attenuated BTEX.