Water flooding has for a long time been employed to improve oil recovery in many oil fields. Formation damage due to water injection was the main issue of water flooding design process for many years and oil companies conducted different compatibility tests between injection water and formation water to eliminate any possibility of formation damage. In recent years, the results of extensive research work demonstrated that alteration of water salinity concentration and composition improves significantly the ultimate oil recovery of water flooding. Up to date there is no universal agreement among the researchers on the mechanism of low salinity flooding. Different mechanisms are proposed in the literature such as wettabiliy modification, fine migration, interfacial reduction, emulsion, and ionic exchange. In this paper an experimental investigation on the possible mechanism of low salinity flooding was conducted. Contact angle changes as function of time, and low salinity water flood experiments using limestone and sand stone rocks for various injection brines were performed. Sand stone and carbonate rocks were obtained from actual Libyan field. High and low salinity waters (223,000 ppm and 20,000 ppm), sea water (49,000 ppm), and water with different sulfate concentrations were employed in this investigation. The results from this work indicated that low salinity flooding can improve the oil recovery of carbonate formation and its performance is function of carbonate type.