Solvent-based recovery processes have gained some advantage over thermal recovery processes under specific reservoir conditions. Solvent-bitumen mass transfer is a diffusion dominated process. The calculation of diffusion coefficients is fundamental for the design of solvent-based recovery processes as it allows us to understand the performance of the process. In a recent work, Babak et al.(1) developed a new slopes and intercept method which was demonstrated to be very robust for the calculation of diffusion coefficients of binary systems. In this paper, the diffusion coefficients of dimethyl ether (DME), pentane, and toluene into two different bitumen systems are calculated using this method as a function of concentration. X-ray computed tomography (CT) is used to obtain the concentration profiles of the bitumen solvent systems. Furthermore, a new modification of Vignes' equation is introduced to predict concentration-dependent diffusion coefficients. This new modification includes the acceleration and deceleration parameter associated with the solvent and bitumen-mass transfer behavior. The developed equation successfully predicts the diffusion coefficients of the studied systems.