We report a study of the oxidative adsorption of butanethiolate on gold from solutions of butanethiolate ranging from 4 x 10(-3) to 7 x 10(-6) M. The mechanism of oxidative adsorption is found to be a function of the concentration of butanethiolate. At concentrations higher than approximately 7 x 10(-4) M, cyclic voltarnmetry and EQCM measurements suggest that the oxidative adsorption proceeds via a fast nucleation and growth mechanism and a slow Langmuir mechanism. In-situ FTIR shows that the resulting monolayer of butanethiolate is organized. The oxidative adsorption from solutions of butanethiolate with a concentration lower than approximately 7 x 10(-5) M is found to be slower and to proceed via a two-step Langmuir mechanism as a result of becoming diffusion-limited. In this case, the in-situ FTIR measurements show that a more disordered monolayer of butanethiolate is obtained. We suggest that the sudden change in the organization of the butanethiolate monolayer is related to the presence of micelles at higher concentration. (C) 2003 Elsevier B.V. All rights reserved.