Abstract: An improved anionic waterflood additive is prepared by alkylating an aromatic hydrocarbon such as benzene with a branched-chain alkene having about 10 to about 35 carbon atoms such as a propylene tetramer dimerization reaction product in the presence of an alkylation catalyst such as AlCl.sub.3 ; sulfonating the thus formed alkylate product 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.