In this study, porosity and permeability values of six different rock samples (three limestone and three sandstone) were determined using thin section analysis technique. The parameters were determined by applying capillary pressure approach through digitally scanned microscopic images. The existence of steam and liquid water in the reservoir make the capillary pressure approach more accurate for the determination of rock properties. The geothermal gradient may also participate in this approach, since the pore diameters of the rock masses change with the changing temperature. A 2-5% increase was observed in porosity values and by applying image analysis technique the permeabilities were found to be around 18% and 10-15% for sandstone and limestone samples, respectively. It was also observed that both porosity and permeability decreased with increasing pressure and depth. A core measurement system (CMS) device was also used to see the effect of pressure and temperature on porosity and permeability values and the results are compared.