It is essential to determine the biodegradation capacity when monitoring or enhancing natural attenuation of petroleum in contaminated aquifers. Here, the concentrations of typical electron donorcontaminants (benzene, toluene, ethylbenzene, and xylene, and chemical oxygen demand) and electron acceptors and byproducts (dissolved oxygen, NO₃^-, Mn²⁺, Fe²⁺, SO₄^2- and HCO₃^-) in a petroleum-contaminated aquifer were determined. The background electron acceptor/byproduct concentrations were determined from the electron donor concentrations, and the acceptor/byproduct distributions were characterized. The biodegradation capacity at each well was estimated using a general geochemical evaluation method. The cumulative probability curve method was used withthe general method to evaluate the biodegradation capacities in the aquifer. The biodegradation rates were determined from the biodegradation capacities and groundwater renewal rates, and different biodegradation zones were identified from the biodegradation rates. The biodegradation capacities of the wells were 36.49~70.05mg/L, and the biodegradation capacity cumulative probability curve for each well fitted the exponential equation F(x)=0.008e^0.07x. The whole-aquifer biodegradation capacity (determined using the probabilities for the different aquifer parts) was 57.83mg/L and the whole-aquifer biodegradation rate (calculated defining the groundwater renewal rate as the groundwater runoff rate, 132m³/d) was 2790kg/a. The downstream source zone was found to have a strong biodegradation capacity. It was concluded that petroleumcontaminants were mainly degraded by the electron acceptors SO₄^2- and NO₃^- reduction. Enhancing SO₄^2- and NO₃^- reduction may be a promising way of managing and remediating the study site.