The purpose of this paper is to present the results obtained by applying six different models to the formalism of the line shapes of 238U in UO 2 developed in the first two papers of this series. These models will increase in complexity, starting from the Maxwell gas treatment, to the harmonic approach for the crystal, the quasi-harmonic model and finally to the totally anharmonic treatment of the crystal, where the peaked unperturbed phonon frequencies w Kj of the crystal will be broadened, due to the phonon widths Г Kj , and the positions will be shifted, due to the phonon shifts Δ Kj from their unperturbed value. The phonon widths and shifts will occur if the cubic and quartic terms are retained in the expansion of the crystal's potential energy in powers of the displacements of the atoms from their equilibrium positions. The line shapes for 238U, based on the anharmonic model, were calculated for the three resonances of 6.65, 80.360 and 787.58 eV at 300, 1200 and 1800 K. It was found that the maximum difference between the line shapes, based on the Maxwell and anharmonic models, occurred in the wings of the resonances. Differences of 12.06, 35.87 and 82.43% were found for the 6.65, 80.36 and 787.58 eV resonances, respectively, at 300 K. These results show that anharmonic effects produce more self-shielding and consequently lower effective capture cross sections in 238U. This, in turn, should lead to better agreement between experiments and calculations of reactor safety parameters. The results for the different models also showed that only the fully anharmonic model is capable of producing less Doppler broadened line shapes, which in turn pointed to the necessity of including anharmonicities in the form of the cubic phonon widths Г Kj, and the cubic Δ Kj , quartic Δ Kj and thermal Δ Kj phonon shifts.