|The sulfur content of crude oil can vary from 0.03 to 7.89 % (w/w). Sulfur emission through fossil fuel combustion is a major cause of acid rain and air pollution. Many governments have recognized the problems and decided to reduce sulfur emissions through legislation. Hydrodesulfurization (HDS) process, operating at high-pressure and high-temperature, is currently employed to remove sulfur from fossil fuels. Recently, Biodesulfurization (BDS) of fuels through microbial activities has been shown to be a potential alternative to HDS, since HDS cannot remove the heterocyclic organo-sulfur compounds such as dibenzothiophene (DBT) which represent about 70% of the sulfur in fossil fuels. A number of microorganisms, particularly Rhodococcus, Bacillus, Arthrobacter, Gordonia and Pseudomonas species have been found to metabolize DBT as a source of sulfur by cleaving the CâS bond of DBT via a sulfur-specific pathway (4S pathway) without affecting the carbon skeleton. In order to compete successfully with HDS, BDS process with a suitable biocatalytic design has to be developed. In literature, very few investigations on BDS process designs and operating costs have been reported but with little success. Lee et al., investigated diesel oil desulfurization in a combination of air-lift/ stirred-tank reactor using cells of Gordonia nitida CYKS1. An air-lift reactor was used to minimize energy costs.