It is well known that Intercrystal scattering (ICS) and the parallax effect are two major resolution limiting parameters in current PET detector designs with block detectors. More recently for the purpose of resolution recovery, investigators and manufacturers have attempted to accurately model these effects into the image reconstruction task. In this study we utilized the MCNP4C Monte Carlo code to accurately simulate and measure ICS and parallax effects in different crystal materials including BGO, LSO, LYSO, LuAP and GSO. The size of the detector module was fixed at a 52mm × 52 mm crystal array. The results showed that by increasing the incidence angle, the percentage of parallax events was considerably increased, while small increases in the ICS fraction were also observed. The point spread function of the various crystal blocks were also investigated, with BGO crystal showing slightly better FWHM values as well as position detection accuracy. The results indicate that the MCNP4C MC code is a useful tool for investigation of photons interaction in PET block detectors in order to accurately model the ICS and parallax behaviors for the purpose of resolution recovery in the new PET image reconstruction algorithms.