The oxidation of was studied at temperatures of 1130°–2160°K and oxygen partial pressures around 3.9 and 20 Torr. The rate of oxidation was monitored with a thermal conductivity cell. Independent measurements were made of net weight gain and quantities of and evolved. Oxidation was shown to be nonpreferential, i.e., zirconium was oxidized at the same rate as carbon. Gas phase diffusion control imposed by the experimental system was frequently encountered. Where it was possible to observe a true chemically controlled reaction rate, the kinetics appeared to be linear. Microscopic examination of the oxidized specimens revealed preferential oxidation along grain boundaries. Between 1130° and 1560°K this preferential oxidation resulted in intercrystalline fracture. At higher temperatures stresses were apparently sufficiently relieved so that the samples remained intact. The oxidation of between 1790° and 2000°K, at oxygen pressures near 10 Torr, was also found to be linear and preferential along grain boundaries.