Thermal equilibria between the heat produced by graphite oxidation and the heat removed by coolant air streams were investigated in the temperature range from 650°C to 735°C. The studies were made on graphite channels whose reactivities differed by a factor of eight. Equilibrium occurs in channels shorter than 10 ft if the numerical value of the reactivity (cal/cm2-sec) is 100-fold greater than the heat transfer coefficient (cal/cm2-sec-°C). The length of channel cooled depends on the heat transfer coefficient and is insensitive to the reactivity when the heat transfer coefficient is numerically equal to or greater than the reactivity of the graphite.