A modified Random Corrugated Pore Structure Model (CPSM) simulating Mercury Porosimetry (MP) hysteresis and entrapment phenomena is proposed. The model have been applied in parametric sensitivity studies and data regression tests by using a single parameter Bell Shape Distribution (BSD) function as the intrinsic pore size distribution (psd). The new CPSM version proved to be superior compared to its original counterpart since it achieves a sensible evaluation of the trapped mercury distribution, enables the construction of a "closed" (zero entrapment) hysteresis loop and makes realistic predictions of the intrinsic pore volume and surface area distributions. CPSM predicted intrinsic psd＇s for reservoir sand stones compare satisfactorily with those measured independently by a photomicrography method. The model also provides the basis for the development of a least square computer code suitable for further improved psd calculations.