This work deals with the prediction of mass transfer of solvents in bitumen in the presence and absence of sand through a unified model that uses magnetic resonance response. information. Experiments were performed with pairs of solvents and bitumen in the presence of sand and without sand. Low field NMR was used to acquire spectra of the migrating solvent in bitumen or oil sand as a function of time. The experimental results of this work, along with data collected previously on similar systems in the Tornographic Imaging and Porous Media Laboratory, were fit together in a one-dimensional Fickian modA The novelty of the presented approach is not only that the new model matches all the experiments to date, but also that this matching can be done independently and without external input parameters. In previous work, matching could only be achieved if the depth of solvent penetration was provided through external measurements. The present model-predicts diffusivities of solvents in bitumen in the presence of sand to be in them same order of magnitude and a bit lower than diflusivities of solvent in bulk bitumen. It is anticipated that this method would be of value when estimates of mass transfer in solvent-based heavy oil processes are attempted in the field.