Silica-supported vanadium oxides (VxOy-silica 600 degrees C) and polymer nanofiber [2-(2'-hydroxy-5'-ethenylphenyl)imidazole (PIMv) and styrene (ST) copolymer]-supported oxidovanadium(IV) ([(VO)-O-IV-p(PIMv-co-ST)]) were synthesized and used as catalysts for the oxidation of refractory organosulfur compounds in fuels in a continuous flow system. Conversion of dibenzothiophene (DBT) to dibenzothiophene sulfone (DBTO2) increased as the flow rate decreased, reaching 100% at flow rates of 0.1 and 0.2 mL/h for (VxOy-silica 600 degrees C) and [(VO)-O-IV-p(PIMv-co-ST)], respectively. This was attributed to improved contact time between the catalyst and substrate, which allowed further oxidation to take place. However, the catalytic activity of VxOy-silica 600 degrees C dropped by 33% after the first oxidation cycle at a flow rate of 0.1 mL/h at 60 degrees C, unlike [(VO)-O-IV-p(PIMv-co-ST)], which maintained its activity at 100% after three cycles. Optimized conditions were employed in the oxidation of a hydrotreated fuel sample (Sasol diesel 500) followed by extraction of the resulting sulfones using acetonitrile. Analyses of the fuel samples using two dimensional gas chomatography coupled to sulfur cheminiluscence and time-of-flight mass spectrometer detectors (GC x GC-SCD and GC x GC-HRT) confirmed the oxidation of organosulfur compounds and removal of the resulting sulfones. This study revealed that [(VO)-O-IV-p(PIMv-co-ST)] was a more robust and more efficient catalyst for the oxidation of organosulfur compounds compared to (VxOy-silica 600 degrees C). Monitoring the V-51 electron paramagnetic resonance signal from the catalysts upon adding oxidant and then substrate showed that the catalysis is of redox nature, involving the V4+ sites.