The effect of a large number of compounds on the cool flame combustion of n-heptane at around 250°C in a static system has been investigated. The organometallic, halogen, nitrogen, and sulfur compounds used (except dimethylamine and α-toluene thiol) had no effect. Alcohols and olefins, however, inhibited the oxidation, increasing the cool flame limits and the “induction period” ( τ) before a cool flame when this occurred. The relative inhibiting efficiency is explained on the basis of the reaction of alkylperoxy radicals with these inhibitors and of the fate of the radicals formed. The temperature rise in the center of the reaction vessel increased exponentially during τ: the rise just before a cool flame occurred remained constant as the total pressure was increased at constant ambient temperature ( T 0) but decreased markedly as T 0 increased from the cool flame temperature limit. The consumption of n-heptane at the end of the induction period and the concentration of higher aldehydes were much greater when isobutanol or cyclohexene was added; and when good inhibitors are present, the flames may, in fact, be due to these higher aldehydes.