A model describing the influence of temperature on the permeability/selectivity tradeoff of polymeric membranes has been developed from fundamental theoretical considerations. This model was used to predict the influence of temperature on upper bound behavior for several gas pairs including O(2)/N(2), H(2)/N(2), CO(2)/CH(4), CO(2)/N(2), H(2)/CO(2), and CO(2)/H(2). The predicted upper bound shifts vertically with temperature, and the direction and magnitude of the shift depend on the sizes and condensabilities of the gases considered. Fair agreement between the model predictions and experimental behavior are realized by allowing three model parameters, two related to diffusivity and one to solubility, to vary with polymer chemistry. The utility of this model is to provide a better fundamental understanding of the influence of penetrant properties and polymer structure on the temperature dependence of transport and properties in membrane gas separation processes and to provide a method to benchmark the gas separation performance of materials, even if the data used for comparison were measured at temperatures far from ambient. (C) 2010 Elsevier B.V. All rights reserved.