An activated carbon adsorption model is presented which predicts performance of adsorption beds using parameters evaluated from batch tests. The proposed dual rate model assumes that a fraction of the total capacity is rapidly utilized in pores which are large with respect to the size of the diffusing species, and that following the rapid uptake phase the remaining capacity is utilized slowly and involves diffusion in pores of similar size to the adsorbate. The model is shown to describe experimental data very well and can be used to suggest why previous efforts at predictive modelling of adsorption beds have had only limited success.