High temperature gas dynamic computational techniques are employed to study microflows in expanding crack channels due to the oxidation of the channel carbon walls. Wall regression rates for three reinforced carbon-carbon (RCC) samples that were tested in a high enthalpy arcjet environment were modeled. The test geometries and flow conditions span flow regimes from the transitional through the continuum, but the same mechanism for wall material loss, atomic oxygen reaction with bare carbon, was utilized in all three cases. The predicted wall degeneration rates were found to agree with arcjet measurements and the general specimen shape change was predicted. Local gas flowfield results were found to affect the oxidation rate in a manner that cannot be predicted by previous mass loss correlations. The method holds promise for future modeling of materials gas-dynamic interactions for hypersonic flight.