Desulfurization of a model fuel system consisting of hexadecane and dibenzothiophene (DBT) by Rhodococcus rhodochrous IGTS8 was demonstrated in a 2-L continuous stirred tank reactor (CSTR). The reactor was operated in a semicontinuous and continuous mode with and without recycling of the model fuel. A constant volumetric desulfurization activity A(t), (in mg HBP L-1 h(-1)) was maintained in the reactor with a feeding strategy of fresh cell suspension based on a first-order decay of the biocatalyst. Maximum desulfurization rates, as measured by specific desulfurization activity, of 1.9 mg HBP/g DCW h were attained. Rates of biocatalyst decay were on the order,of 0.072 h(-1). Theoretical predictions of a respiratory quotient (RQ) associated with this biotransformation reaction agree well with experimental data from off-gas analysis. In addition, the ratio of the specific desulfurization activity a(t), (in mg HBP/g DCW h) of recycled and fresh biocatalyst was determined and evaluated.