Having reliable estimate of gaseous-solvents molecular diffusion coefficients in heavy oil and bitumen is a requisite for analysis and design of gas injection and solvent-based recovery techniques. Nevertheless, diffusion coefficient is not measured accurately unless all the other contributing mass transfer parameters are considered, included in the modeling, and estimated correctly. These parameters are gas solubility and the interface resistance, of which the latter is represented by mass transfer coefficient. In this work, an analytical model is introduced in conjunction with an inverse technique to obtain these three abovementioned parameters using pressure decay technique. One of the objectives of this work is characterization of interface resistance both numerically and physically. In this work, we will evaluate one of the possible reasons for the presence of resistance at the gas-oil interface.