The reaction of benzene with oxygen atoms produced by mercury photosensitized decomposition of nitrous oxide has been studied in a circulating system at room temperature. The main reaction product is a non-volatile material probably largely aldehydic in character. This is tentatively assumed to result from the rearrangement and polymerization of the initially formed adduct. Smaller amounts of phenol and carbon monoxide are also formed. The rate of formation of carbon monoxide decreases with increasing pressure, suggesting an energy-rich precursor.Oxygen atoms react with benzene much more slowly than with olefines. At 120° cyclopentene reacts about 150 times more quickly than benzene. The activation energy of the reaction of oxygen atoms with benzene has been estimated at 4.6 to 4.9 kcal/mole, with an uncertainty of about 0.7 kcal/mole.