ABSTRACT Using simple models of pore systems in conjunction with percolation theory concepts, relationships between the residual oil saturation at very low flooding rates and three petrophysical parameters, the porosity, the formation resistivity factor and Archie's lithologic exponent are found. Experimental data using air/liquid countercurrent imbibition along with routine petrophysical measurements on a set of clean, well-sorted sandstones and various carbonates confirm these relationships. Empirically, the best correlation for the residual oil saturation is with the porosity, although the formation resistivity factor also provides a good correlation.