Mineral oil diffusion in styrene-butadiene polymer films was investigated with a simple gravimetric sorption method. Over the selected range of temperatures and film thicknesses for which sorption tests were performed, the diffusion process is described in terms of Fick's third law. Polymer dissolution was found to compete with the diffusion process especially at high temperature. Possible interference due to dissolution on data generated using a gravimetric method, resulted in an estimation of apparent activation energy using diffusion coefficient set calculated with Crank's half-time relationship. The mineral oil diffusion activation energy was found to be relatively high compared with those of hydrocarbons diffusing in natural and synthesized rubbers or cross-linked polybutadiene as reported in the literature. The influence of polymer T-g, crosslinking density, and polarity on mineral oil ability to penetrate polymer film was evaluated in terms of percent weight increase over time. Maximum absorption after 60-min sorption time linearly correlates with mineral oil absorption rate for polymers prepared with different structures. This linear relationship suggests that diffusion of solvent in styrene-butadiene polymers reveals the macroscopic composition and structural polymer modification rather than local changes. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 111: 2886-2891, 2009