Numerical simulations of a superfilling model are shown to be consistent with experimental results obtained in the absence of an inhibiting, leveling agent that can be described by a diffusion-adsorption mechanism. The model, which assumes that superfilling is caused by accumulation of the adsorbed accelerator at the feature bottom as surface area available for deposition within a feature shrinks, also predicts the formation of bumps. Because the model parameters have not been independently measured, the details of the model may need further refinement, but the general approach appears feasible.