Résumé : By comparing theoretical and experimental excitation functions of evaporation residues resulting from the same compound nucleus or heavy and superheavy nuclei, it is possible to understand the effect of the entrance channel and the shell structure of reacting nuclei on the fusion mechanism. The competition of complete fusion with the quasifission process is strongly related to the intrinsic fusion barrier Bfus* and the quasifission barrier Bqf, as well as the size of the well in the nucleus-nucleus potential. In our calculations of the excitation functions for capture, fusion, and evaporation residues, we use the relevant variables such as mass asymmetry of nuclei in the entrance channel, potential energy surface, driving potential, spin distribution, and surviving probability of compound nucleus that are responsible for the mechanism of the fusion-fission process. As a result, we obtain a beam energy window for the capture of the nuclei before the system fuses and the Γn/Γf ratio at each step along the deexcitation cascade of the compound nucleus. Calculations performed in the framework of the model taking into account the nuclear shell effect and shape of colliding nuclei allow us to reach useful conclusions about the mechanism of the fusion-fission process and the production of the evaporation residues. We analyze the 40Ar + 176Hf, 86Kr + 130Xe, and 124Sn + 92Zr reactions leading to 216Th*; the 32S + 182W and 60Ni + 154Sm reactions leading to 214Th*; the 48Ca + 248Cm reaction leading to the 296116 compound nucleus; and the 48Ca + 249Cf reaction leading to the 297118 compound nucleus. © 2003 MAIK "Nauka/Interperiodica".