This paper presents a data analysis approach to determine Archie parameter a, m and n from standard resistivity measurements on carbonate rocks core samples from Omani oil fields. The constants a and m were determined from core derived porosity data and the corresponding formation resistivity factor under different overburden pressures. Saturation exponent n of Archie's formula was estimated by measuring resistivity index for different brine saturations. The exact determination of Archie parameters is of paramount importance for the evaluation of oil reservoir rocks. Small change of a, m and n could produce a dramatic difference in the hydrocarbon reserve estimation processes. The core analysis presented in this study for carbonate rocks showed that a is in the range of 0.74 to 1.81 with an average of 1.12 and m varies from 1.41 to 2.79 and giving an average of 2.03. Saturation exponent n has a range of 1.83 to 2.59, with an average of n 2.08, indicating that the studied reservoir is predominantly water wet. Cementation factor m and formation factor coefficient a were tested under different overburden pressure conditions. It is found that m and a are sensitive to the change of the applied overburden pressure.