Residual volatile hydrocarbons in bitumen constitute a potential source of air pollution. Diffusivities of volatile components in bitumen are needed to assess the extent of environmental damages that could result from bitumen spill or working loss of vapour to the atmosphere. Knowledge of solvent dispersion is also required in the recovery of viscous bitumen by solvent displacement. This paper discussed the de-coupled transfer model developed by Tang and Zhang and its limiting solution. Fu and Phillips' diffusion data were re-interpreted based on the limiting solution with delay time correction. The diffusion coefficients of hexane iso-hexane, cyclo-hexane and toluene at 25 degreesC were found to be 8.6 x 10(-8) cm(2)/s, 6.3 x 10(-8) cm(2)/s, 2.4 x 10(-8) cm(2)/s and 6.8 x 10(-8) cm(2)/s, respectively. Improper use of the limiting solution could lead to 25% over-estimates of diffusion coefficients.