The oxidation of toluene and ethylbenzene has been studied in a static system using a spherical reaction vessel (700 ml.) over the temperature range 300 to 500 degrees C, and at total pressures up to 600 mm. Cool flames were observed in the oxidation of both hydrocarbons, but only the reaction of ethylbenzene gave rise to a 'blue' flame at higher temperatures. With neither hydrocarbon did periodicity in light intensity, or pressure pulses, occur. The ignition diagrams for 4 to 1 fuel + oxygen mixtures have been mapped out. With ethylbenzene, the cool flame was maintained in a flow system, its spectrum was photographed and shown to be similar to that of fluorescent formaldehyde. The products of the reaction contained acetophenone, benzaldehyde and benzoic acid, phenol, quinol, hydrogen peroxide and methoxyhydroperoxide. The results have been compared with corresponding data for the oxidation of paraffin hydrocarbons, and it is concluded that, with both aromatic compounds, the processes allowing the possibility of cool-flame formation are themselves secondary in nature.