Publisher Summary This chapter discusses the use of surfactants in oil recover. Surfactant molecules are composed of two portions called lipophilic and lipophobic groups. Lipophilic group has sufficient solubility in the solvent and always tends to bring the entire molecule into solution, whereas lipophobic group is rejected by the solvent, because it has less affinity for the solvent molecules and tends to expel entire molecules from the solution. This lipophilic–lipophobic structure is known as “amphipathic structure.” If the force because of the lipophobic group predominates, the surfactant molecules tend to concentrate at an interface and at least a part of the lipophobic group is not in contact with solvent molecules. The lipophilic group usually consists of a long hydrocarbon chain. A polymer can also act as a surface-active molecule if it has two functional groups, one lipophilic (solvent loving) and the other lipophobic (solvent hating). The surface properties of a surface-active compound are controlled by the balance between its lipophilic and lipophobic characteristics. In this chapter, the classification of enhanced oil recovery (EOR) surfactants is discussed. Mechanism of oil displacement by surfactant flooding is explained. Ultralow interfacial tension in relation to oil displacement by surfactant flooding is described in the chapter.