The performance of simulated annealing (S-A) in nonlinear kinetic parameter estimation was studied and compared with the classical Levenberg-Marquardt (L-M) algorithm. Both methods were tested in the estimation of kinetic parameters using a set of three kinetic models of progressively higher complexity. The models describe the catalytic wet air oxidation of phenol carried out in a small-scale trickle bed reactor. The first model only considered the phenol disappearance reaction, while the other two included oxidation intermediate compounds. The number of model parameters involved increased from 3 to 23 and 38, respectively, for the three models. Both algorithms gave good results for the first model, although the L-M was superior in terms of computation time. In the second case the algorithms achieved convergence, but S-A resulted in a better criterion and kinetic parameters with physical meaning. In the more complex model, only S-A was capable of achieving convergence, whereas the L-M failed. For the second and third model the solution of S-A could be further improved, when used as an initial guess for the L-M algorithm.