Measuring the solubility and diffusivity of methane in porous media saturated with oil is critical for analyzing the process of solvent-based recovery of heavy oil reservoir. In this study, a modified pressure-pulse decay (PPD) method is presented to measure the mass transfer coefficients of methane in porous media saturated with heavy oil as well as the solubility and diffusivity of methane in bulk oil under the same experimental conditions as those used in a comparison. The experiments are conducted under constant boundary pressure in a PVT cell, and the pressure is controlled using an auto pump, which continuously compresses the volume of an intermediate container. The accumulated volume change instead of the pressure change is recorded with time. The nonequilibrium boundary condition (BC) model is used to analyze the experimental process. The general solution of the mathematical model is derived using the Laplace transform and the approximate analytical solution of the accumulated dissolved gas is further presented for post processing of the experimental data. The mass transfer coefficients are estimated through using a multilevel single-linkage (MLSL) method to match the approximate solution with the recorded experimental data. The estimation of the parameters shows that the mass transfer coefficients are pressure dependent and that a high boundary pressure contributes to the mass transfer of methane in heavy oil due to a reduction in viscosity or density. The interface mass transfer coefficient (K-int) and interface saturated concentration (C-int) in porous media saturated with oil and bulk oil are almost the same under the same experimental conditions. The sensitivity analysis shows that the increase of the effective diffusion coefficient (D-eff) and kin, contributes to enhancing the rate of mass transfer in the oil phase and that Henry's law constant (H) has no effect on the equilibrium time but only affects the initial saturated concentration at the interface or the total dissolved gas. The modified PPD method is robust, efficient, and easy to use in the laboratory.