Modification of injection water salinity to improve oil recovery is not a new idea and the process has been investigated as far back as the 70's prior to the use of other chemical processes to improve oil recovery. In practice in planning water flooding project oil companies focused only on the compatibility of injection water and formation water issue to eliminate any possibility of formation damage. Many investigators recently had focused their research on the role of water salinity alteration to improve oil recovery. A number of possible mechanisms concerning alteration of water flooding salinity have been proposed in the literature. This project describes an experimental investigation of contact angle changes as function of time, and water flood performance using limestone and sand stone rocks for various injection brines. Carbonate rocks, sandstone rocks obtrained from a Libyan oil reservoir, high salinity water, sea water, low salinity water, and water contains different sulfate concentrations were employed in this study. The results of this research will shed more light on the mechanism of modified salinity flooding (MSF™) and will help operating companies to better plan water flooding process.