Wettability has, in recent years, been recognized as one of the most important parameters for a reservoir. The industry is privileged to have an excellent series of review articles by Anderson (1986-1987), which provides exhaustive discussions on how wettability affects other reservoir parameters. The only scientifically proper method of measuring wettability is to obtain a contact angle between the two fluids and the rock. If the contact angle measured through a fluid is less than 90° a neutrally wet situation is said to exist. However, direct measurements are rarely practical with actual reservoir materials. Actual reservoir materials are sometimes approximated by "pure" smooth surfaces: glass (silica) for sandstones or calcite crystals for carbonates. When two immiscible fluids are in contact, due to the interfacial tension forces, the interface will be curved with higher pressure on the concave side than on the convex side.