Photooxidation of gaseous diethyl sulfide (DES) at a concentration in the order of hundreds of ppm was carried out in a flow reactor over four different samples of TiO2 under ambient conditions. (C2H5)(2)S-2, CH3CHO, CH3CH2OH. C2H4, and CO2 were detected as the major products in gaseous effluent of the reactor. The trace products in gas phase included CH3COOH, C2H5SC(O)CH3, and SO2. All the catalysts studied showed deactivation with a characteristic temporal range of 100-300 min. The surface products extracted by isopropanol included (C2H5)(2)S-2, (C2H5)(2)S-3, (C2H5)(2)SO, (C2H5)(2)SO2. and C2H5SCH2CH2OH. The residual activity was the highest for TiO2 Hombikat UV 100. At relatively low light intensities (1.1 mW/cm(2)), the increase in humidity from less than 1 % to similar to 20 and similar to 60% resulted in the increase of the quantities of diethyl sulfide converted. However, at relatively high light intensities (11 mW/cm(2)) such an increase in humidity had an adverse effect on the conversions of diethyl sulfide. The quantities of (C2H5)(2)S converted and the products formed correlate well with the specific surface area of the TiO2 samples, thus indicating the importance of surface reactions in gas phase photooxidation of diethyl sulfide. Additions of H2O2 in the reactor feed stream increased the rate of diethyl sulfide destruction, but also altered the product distribution throughout the reaction time. Steps of the reaction mechanism are proposed to explain the formation of this set of products and observed kinetic dependencies. The main routes of this: mechanism are C-S bond cleavage, S-oxidation, and C-oxidation.