Book excerpt: Surface chemistry has a great effect in enhancing oil recovery. For oil-wet sandstone reservoirs, low salinity waterflooding (LSWF) is effective as it can alter rock wettability and reduce the oil/water interfacial tension. LSWF application is related to rock’s clay content and type. Clay hydrocarbon bonding can be formed through many mechanisms such as van deer waals forces and ionic bridge. LSWF effect is to weaken these bonds through two main mechanisms, Double Layer Expansion (DLE) and Multicomponent Ionic Exchange (MIE). Two fields (S and D), in Egypt’s Western Desert, have depleted strongly oil-wet reservoirs with similar rock and fluid properties. Field (S) is flooded by low salinity water (LSW), while Field (D) is flooded by high salinity water (HSW). Fortunately, the water source for Field (S) flooding is a LSW zone, which has a salinity +/- 5000 ppm as total dissolved solids (TDS). The formation water salinity was +/- 25,000 ppm as TDS. Field (S) lab experiments showed good compatibility between injected LSW, formation water and rock minerals. XRD and SEM indicate calcareous cementation with detrital clays content around 5%. Kaolinite is the common clay type, which has a low cation exchange capacity. For Field (S), the estimated ultimate recovery (EUR) is 46%, while EUR for Field (D) is 39%. One of the main causes of this increase in Field (S) is LSWF application.