There are numerous models describing solute diffusion in polymer solutions. An analysis of these models demonstrates that none can provide a consistent explanation of the phenomenon observed for solutes that can be modeled as essentially solid spheres, For this reason, a new model based on a physical obstruction approach is presented. In this model, solute movement in the presence of polymer chains is assumed to be governed by the probability of the solute molecule encountering a series of openings between the chains larger than its hydrodynamic radius. The model is tested against data taken from the literature for a series of polymer solutions and solute probes and found to provide good agreement to the effects of solute size, polymer concentration, and polymer flexibility.