This paper examines experimentally the effects of fractional wettability on the saturation exponent of Archie＇s equation, also commonly known as the resistivity index exponent. A four-electrode experimental setup has been used to measure glass-bead-pack resistivity using both the dynamic displacement technique and the steady-state technique. Mixtures of oil-wet and water-wet beads were used covering the entire wettability spectrum. Wettability of the glass beads was reversed using both asphaltic crude oil and Quilon-C in isopropyl alcohol solution. Similar experiments were also duplicated on Berea sandstone core samples. A linear relationship between the resistivity index exponent and fractional oil wettability was observed. This exponent seemed to vary between values of approximately 2.0 for water-wet conditions and approximately 5.0 for oil-wet conditions for both glass-bead packs and Berea sandstone rock samples. This dependence between degree of wettability and saturation exponent is used to estimate in-situ reservoir rock wettability by combining data from EPT and resistivity logs for the same formation.