Phenols, carboxylic acids and other water-soluble compounds in bitumen constitute a potential source of groundwater pollution. To assess the extent of damages that could result from a spill, a water extraction method was used to determine the molecular diffusion of phenol in bitumen. This method involves the diffusion of phenol through bitumen into the flowing water in a well-stirred cell. From the phenol concentration in water, the phenol flux and hence the phenol diffusion coefficient in bitumen can be deduced. An approximate dimensionless solution was obtained by de-coupling the diffusional flux from the concentration buildup in water. The phenol diffusion coefficient was determined to be 4.0 +/- 0.3 x 10(-8) m(2)/s at 22 degreesC. The derivation and the properties of the dimensionless solution were also discussed in the paper.