Nonequilibrium state is a universal phenomenon in gas injection development. However, in previous researches and applications, it tends to be regarded as quasi-equilibrium state, or even equilibrium state. Based on research work by pioneers, a simple model for measuring diffusivity of N2 in oil has been developed. In addition, laboratory experiments were performed in this study. Results indicate that an infinitely thin layer exists between N2 zone and oil zone in the pressure-volume-temperaturacelda (PVT) cell. Gas and oil molecules will slowly diffuse into one another across the sharp interface by convection, dispersion, and diffusion. Viscosity and gas oil ratio (GOR) are two important parameters representing the phase behavior features of the N2 and oil system. These dependent variables are related to parameters like pressure, temperature, and oil viscosity.