The diffusion coefficient of vaporized solvents in bitumen is an essential parameter in the design and performance evaluation of solvent-assisted thermal recovery methods. The reported measurements of solvent diffusion coefficient are relatively scarce, especially at the high temperatures. In this study, a new constant-pressure experimental technique for one-dimensional diffusion tests, which accounts for the bitumen swelling and density change, was developed. The experimental rig enables measurement of diffusion coefficient of vaporized solvents in bitumen at high temperatures encountered in solvent-assisted thermal recovery methods. The technique involves accurate monitoring of the swelling height during isothermal and isobaric dissolution of a vaporized solvent in a liquid column of the oil. Several analytical and numerical models have been reported as forward models for estimation of diffusion coefficient from experimental data based on various assumptions. However, an important physical mechanism, the swelling-induced advective transport has not been considered in the previous studies. In this study, an analytical model is developed to determine the molecular diffusion coefficient of gaseous solvents into the bitumen, including the swelling effect, density change and advective transport. The required experimental data for determining the diffusion coefficient with this analytical model are the swelling height (gas-liquid interface movement) with time, during the dissolution of a gaseous solvent at constant pressure and temperature in a liquid column. The diffusion coefficients of propane, butane, pentane, hexane and heptane, were measured at temperatures varying from 90 C to 195 C. A modified correlation of diffusion coefficient with bitumen viscosity and solvent-bitumen mixture viscosity was developed based on the experimental results from this study and reported data from other studies. The new correlation provides a simple and reliable estimation of the diffusion coefficient of vaporized solvents in heavy oils and bitumen.