Information about diffusion in solvent+bitumen/heavy oil mixtures is useful for the design of solvent-assisted recovery processes as a key parameter in reservoir simulation models. Reliable mutual diffusion coefficient measurements for these systems present significant challenges. In this article, experimental techniques for the study of diffusion in liquid solvent+bitumen/heavy oil systems are critically reviewed, and the strengths and weaknesses of each method are highlighted. Despite considerable progress in this area with the application of state-of-the-art techniques, such as X-ray computer-assisted tomography measurements, additional work is needed to measure the composition profiles in these opaque systems more precisely and to analyse the measured concentration profiles more conveniently.