Abstract: Initial oil saturation of low resistivity oil layer play a critical role in identification of oil/water layers. It was commonly calculated by using electric properties data, but many oil layers have been bypassed when the calculation results of Archie's formulas were used as discrimination standards. This paper presents a method which calculates oil saturation by using core analytical data and in combination with analysis and calculation of nonlinear regression of capillary pressure. This method establishes relations between capillary pressure, core porosity and oil column and builds V Hg - Φ regression equation through statistical analysis. Relatively real initial oil saturations of low resistivity oil layers can be achieved. Field application shows that it is reliable.