With increasing energy demand and high cost of conventional light oil production with low recovery, oil companies are now forced to search for unconventional oil as a major future source of hydrocarbon. As a result a variety of enhanced oil recovery (EOR) methods have been developed for increasing recovery after primary and secondary methods. After primary and secondary methods two thirds of the original oil in place (OOIP) in a reservoir is not produced and still pending for recovery by efficient EOR methods. The supplied energy may intend to maximize oil recovery by means of oil swelling, lowering of interfacial tension (IFT), improving mobility ratio, rock wettability modification, oil viscosity reduction and favorable phase behavior. This book contributes knowledge of improved study on EOR by chemical method dealing with microemulsion phase behavior and its physicochemical properties, IFT reduction mechanism, wettability alteration by different surfactants, additional oil recovery by microemulsion flooding and finally adsorption experiments for economic feasibility study.