Alkyl ethers have been used as gasoline additives (oxygenates) to reduce the level of CO and VOC from the emissions of motor vehicles. Large quantities of these oxygenates have been spilled into groundwater and drinking water supplies creating a significant risk to the environment. These compounds can be decomposed by hydroxyl radical generating technologies. The TiO2 photocatalytic mediated reaction pathways were defined and reaction mechanisms were proposed to explain the formation and disappearance of several intermediate products. Based on a series of substrates, a structure-reactivity relationship was proposed for predicting the reaction pathways. The results from homogeneous (radiolysis) and heterogeneous (TiO2 photocatalysis) generation of hydroxyl radicals were compared to assess the role of the catalyst surface in the reaction pathways. This is an abstract of a paper originally presented at the 225th ACS National Meeting (New Orleans, LA 3/23-27/2003).