The modern petrochemical industry relies on several hydrocarbon raw materials: methane, ethylene, propylene, butene, higher olefins, and the aromatics. Some of the most important processes that such raw materials are initially subjected to are oxidation reactions[1]; for example, methane is converted to acetylene, ethylene to ethylene oxide, and propylene to acrolein, acrylic acid, or acrylonitrile. The complete oxidation of any of the hydrocarbons being favored thermodynamically, all partial oxidation reactions are kinetically limited, the nature of the products being determined mechanistically. In heterogeneous catalytic oxidations the mechanism essentially involves interaction between a hydrocarbon and surface oxygen species. In the case of the oxidation of ethylene to ethylene oxide, carbon dioxide, and water, silver is unique in giving a high selectivity to ethylene oxide. We believe it is the type of adsorbed oxygen species involved in the interaction that determines the course of the reaction and hence the selectivity.