The bacterial strain, namely, Rhodococcus sp. (JUBT1) isolated from petrol/diesel station, has been used for different model organo-sulfur compounds like, DBT, alkylated DBT, etc., which usually remain unchanged during the conventional hydro-desulfurization of the diesel fraction. The initial concentration of organo-sulfur compounds has been varied in the range of 100-1000mg/dm(3). Under the present experimental range the bacterial growth has been observed to follow Haldane type kinetics characterizing the presence of substrate inhibition. Although the growth of the bacterial strain is of substrate-inhibited type for all model organo-sulfur compounds, used as limiting substrates, the extent of inhibition is, however, different. For the same values of initial concentrations the inhibition is more pronounced for the organo-sulfur compounds containing larger number of alkyl substitutions. The values of intrinsic exponential growth phase kinetic parameters like lt mu(max), maximum specific growth rate, K-S, half saturation constant, K-Si, inhibition constant, have been determined using each organo-sulfur compound of different number of alkylation as limiting substrates. Relative change in the value of kinetic parameters has been correlated to the number of substitution. A mathematical model has been developed to predict the conversion of sulfur during batch type bio-desulfurization of model compounds as well as diesel having known distribution of organo-sulfur compounds. The predictions of the model have been compared with the experimental results satisfactorily. (c) 2005 Elsevier B.V. All rights reserved.