Monte Carlo (MC) simulations, based on the lattice-gas approach, of the coverage-dependent chemisorption kinetics and initial oxide formation on Al(111) are presented. Three different adsorption mechanisms for the early chemisorption phase, discussed in the literature, are considered: (i) "hot" dimer dissociation; (ii) abstractive dissociation; and (iii) "normal" dissociation without "hot" fragments. The simulation results are compared with the experimental scanning tunnel microscope (STM) results by Brune [J. Chem Phys. 99, 2128 (1993)]. The best agreement between the MC simulations and the STM results is obtained with the hot dimer mechanism.