The mobility (diffusion and trapping) of the heavy rare gases Kr, Xe, and Rn in pure and doped NaCl single crystals was measured following ion bombardment to various integrated doses (10 8 to 2X10 16 ions/cm 2 ) and at energies between 30 and 500 keV. No obvious effect of doping on release was found. At low gas concentrations, release was compatible with volume diffusion yielding an activation enthalpy, ΔH, of 1.5 ±0.2 eV. This value was obtained for both very low and very high bombardment energies (≈ 1 and 500 keV) thus indicating that the same release mechanism is operative near the surface and in the bulk material. For this release mechanism, a mobility in small vacancy clusters was suggested. At higher gas concentrations, the release was shifted towards higher temperatures. This retarded release was explained by transient trapping, i. e. by gas-gas or gas-damage interactions, and was shown to have a partially single jump character. Again, the result was the same for low and high bombardment energies.