This study presents interpretation results of core and log data measurements of four wells (B2-NC-74A, B5-NC-74A, B6-NC-74A and B8-NC-74A) situated in Sirte Basin of Libya. Measured data were analysed for log calculated water saturation essential for proper evaluation of oil volumes. It illustrates the effect of true core derived exact formation properties, such as saturation exponent(n), cementation exponent(m), and Archie parameter (a) on water saturations and reservoir bulk volumes calculated from default parameters and formation log data. An initial conventional analysis using Interactive Petrophysics (IP) software programme for saturation with default values “a”, “m” and “n” of 1, 2 and 2 presented standard water saturation and bulk volume oil results. Working data is later reprocessed with true formation average “a”, “m” and “n” values from core data measurements for comparative analysis. Following reprocessing and complex interpretation of working data, result interpretation demonstrates that proper and accurate evaluation of initial water saturation is significantly influenced and controlled by deviation of formation values “a”, “m” and “n” from the standard assumed default values of 1, 2 and 2. Average “a”, “m” and “n” values of core data provided water saturation and oil volume results that differed from those of default parameter set. Oil volume calculations showed strong relationships with saturations as demonstrated by applicable crossplots. Wells with decreased “n” values showed increase in oil volumes while wells with higher “n” values had much water and less oil in them. C