Abstract: In cosurfactant enhanced alkaline flooding of a formation containing anhydrite, the pH of the flooding material is maintained at a high lvel by the addition of an alkali metal sulfate or ammonium sulfate.

Abstract: An improved anionic waterflood additive is prepared by partially chlorinating a normal alkane having about 10 to about 18 carbon atoms to about 2 to about 15 weight percent chlorine content, employing the chlorinated alkane to alkylate an aromatic hydrocarbon, such as benzene; sulfonating the thus formed alkylate or a fraction thereof to form a sulfonic acid; converting the sulfonic acid to a sulfonate by reacting with a base component, such as an alkali metal hydroxide, ammonium hydroxide, or an alkali metal carbonate; and overbasing the sulfonate by admixing with an excess of base component such that the ratio: "weight of excess base component/weight of sulfonate" is about 0.03 to about 3.0. The anionic waterflood additive is injected into a petroliferous formation, the formation is waterflooded, and oil is recovered.