The reactions of three aromatic hydrocarbons, benzene, toluene, and styrene, with oxygen in a radiofrequency (rf) plasma were investigated. Benzene was oxidized to yield phenol as a single volatile organic product. Similarly, toluene gave the ring oxidation products, cresols, as well as considerable amounts of methyl oxidation products, consisting mainly of benzaldehyde and benzyl alcohol. In contrast, the oxidation of styrene took place predominantly on the olefinic double bond to produce styrene oxide. On basis of the products and effects of reaction variables, rf power and flow rates of hydrocarbons and oxygen, on the reaction rate, the oxidation mechanism was discussed, particularly focusing on the intermediate species responsible for the formation of major products.