[en] The effects of oxidizing atmosphere and temperature on the reactivities and strengths of PGX, H451, and IG-11 were examined. Preliminary measurements of the oxidation kinetics of these graphites in H₂O-, CO₂- and O₂-containing atmospheres indicated that the reactivities of H451 graphite toward O₂ and H₂O are quite similar to those of IG-11 graphite. The apparent activation energy for oxidation of these in O₂ were estimated to be approx. 175 kJ/mol while that in H₂O is probably approx. 200 kJ/mol. The apparent activation energy of IG-11 graphite oxidized in CO₂ is 255 +- 18 kJ/mol. PGX graphite was found to be quite variable in its reactivity toward H₂O. A linear dependence with [Fe] was determined, but other intrinsic properties were found to affect its absolute reactivity by as much as a factor of X50