Archie found an empirical equation for consolidated sandstones relating several formation parameters, such as, porosity and water saturation. Although Archie equation is usually used by petroleum engineers, it is not easy to apply it for carbonate rocks, because formation parameters (m, n) are functions of changes in the pore geometry, clay content, tortuosity of the pores, as well as formation pressure. The sandstone, limestone and shale existence in Asmari formation of Gachsaran oil field are necessitated for determination and correlation of m and n parameters in Archie equation. The real log evaluation data of the Gachsaran oil field wells are used to find a more precise correlation between formation resistivity factor and formation water saturation.