The objective of this work is to explore the potential of carrying out oxidative desulfurization using air as an oxidant. The liquid fuels to be desulfurized were first contacted with air to produce hydroperoxides in situ, which were then used as selective oxidants to oxidize the sulfur compounds. Unsupported CuO was tested as a catalyst for producing hydroperoxides in the fuel at 120 degrees C in the presence of air. Air oxidation was also carried out in the presence of Al2O3-supported CuO and also noncatalytically. Unsupported CuO was substantially more active than the other two cases. The yield of the hydroperoxides depends strongly on the catalyst and the reaction temperature; the yield decreased in the order of 120 degrees C > 140 degrees C >> 100 degrees C but the rate of oxidation to produce hydroperoxides decreased in the order of 140 degrees C > 120 degrees C >> 100 degrees C. It was found that more hydroperoxides could be generated in diesel fuel than in jet fuel, which might be related to the higher concentration of alkyl aromatics in diesel fuel when compared to JP-8 jet fuel. The hydroperoxides generated in situ were then used to oxidize the sulfur compounds in the fuel in the presence of SiO2-supported MoO3 catalyst. Hydroperoxides generated in situ were effective in oxidizing the alkyl-substituted benzothiophene and dibenzothiophene present in jet and diesel fuels to their corresponding sulfones which were then removed by adsorption on beta zeolite. On the other hand, the amount of cumene hydroperoxide required per mole of S for oxidation to sulfone was 1.5 and 10 times higher than the stoichiometric amounts for JP-8 jet fuel and diesel fuel, respectively. This study demonstrates that oxidative desulfurization can be effectively carried out by using air as an oxidant for generating hydroperoxides in situ, which can then be used to selectively oxidize the sulfur compounds to sulfones, thereby eliminating the need for use, storage, and handling of expensive liquid-phase peroxide oxidants.