The efficiency of the photocatalytic destruction of methyl tert-butyl ether (MTBE) in the gas-phase using UV light and titanium dioxide was studied. TiO2 was coated on the inner side of the photoreactor. Specifically, the effect of residence time (0.17-2.22 min), MTBE concentration (500-5000 ppm), oxygen concentration (0-20,000 ppm) and water vapor on MTBE conversion was examined. Acetone and tert-butyl formate were detected in the photoreactor effluent. The formation of by-products from MTBE decomposition was determined with gas chromatography-mass spectrometry. The residence time affected dramatically the MTBE photo-oxidation as well as by-products existence and configuration. The increase in MTBE concentration at the reactor inlet and the addition of water vapor to the reactants resulted in decreased MTBE conversions. Increasing oxygen concentration up to 10,000 ppm enhanced the photocatalytic process but a further increase to 20,000 ppm had an adverse impact on MTBE decomposition. In all cases, the by-product formation profiles were extremely dependent on photocatalysis parameters studied.