The various effects of a diffusion process on estimation of a gas-diffusion coefficient were studied in the complete paper. Considering both classical and recently attempted boundary conditions, the effects of taking into account the nonequilibrium nature of a diffusion process on estimation of mass-transfer parameters using pressure-decay data of carbon dioxide (CO2), methane (CH4), ethane (C2H6), and nitrogen (N-2) dissolution in Athabasca bitumen at two different temperatures were found to be negligible, considering the gas/oil-interface resistance on calculated values of diffusivities.