Pore sizes are on the order of nanometers for shale and tight rock formations. Such small pores can affect the phase behavior of in-situ oil and gas owing to increased capillary pressure. Not accounting for increased capillary pressure can lead to inaccurate estimates of ultimate recovery. In this research, capillary pressure is coupled with phase equilibrium equations and the resulting system of nonlinear fugacity equations is solved to present a comprehensive examination of the effect of small pores on saturation pressures and fluid properties. The results show, for the first time, that accounting for the impact of small pore throats on PVT properties explains the inconsistent GOR behavior observed in tight formations. The small pores decrease bubble-point pressures and either decrease or increase dew-point pressures depending on which part of the two-phase envelope is examined.