The triple differential cross section for ionization of the inert gases He, Ne, Ar, Kr, and Xe in energy-sharing perpendicular plane geometry is investigated. Encouraging agreement with recent experiments is found using the distorted-wave Born approximation (DWBA). Mechanisms are discussed which explain the He and Ne data but which seem to be masked by the greater distortion effects in the heavier targets. The inclusion of postcollisional interaction is explored using Gamow, N ee , and Ward-Macek, M ee , factors. While both help to improve the shape of the cross section for He and Ne at the lower energies, they are not successful for the other targets, and both factors prove to be too strong for all the inert gases with increasing impact energy. It is well known that N ee destroys normalization. Comparing DWBA + M ee results with some absolute experimental points at 1 and 2 eV indicates that it is also not to be trusted on normalization. An interesting situation with Ar is highlighted near 25 eV, where the cross section may be tending towards a strong interference minimum or zero.