The dynamics of adsorption of benzene dissolved in supercritical carbon dioxide on activated carbon were studied by analysis of breakthrough curves in the nonlinear region of the adsorption isotherm, The column was long enough to ensure constant pattern conditions, and the shapes of the experimental breakthrough curves were used for identification of the controlling mass transfer processes, The effects of intraparticle diffusion and external mass transfer were investigated by numerical solution of the corresponding differential equations, Surface diffusion was found to be the main transport mechanism inside the adsorbent particles. No considerable variation of the effective surface diffusivity was observed in the range of experimental conditions, and the measured values are in the order 10(-10)m(2)/s.