A robust and reliable experimental approach was developed and implemented for measurement of the concentration-dependent molecular diffusion coefficient of gaseous solvents in bitumen mixtures. The developed methodology relies on accurate measurement of the rate of gas injection throughout the constant-pressure diffusion experiment. The experimental setup was then used for studying the concentration-dependent behavior of the diffusivity of gaseous dimethyl ether (DME) in bitumen at 2.76 MPa and 110°C. The estimated values of the molecular diffusion coefficient are in the range of ~1.79-3.72×10−9 m2/s increasing with the initial concentration of DME in bitumen. The results indicate that there exists a noticeable dependency of the molecular diffusion coefficient on the concentration of the solvent in bitumen. The developed methodology finds application in estimation of the concentration-dependent molecular diffusion coefficient of gaseous solvents in bitumen.