a composition capable of selectively plugging highly permeable zones in a subterranean formation . the composition forms a gel subsequent to its injection into the formation via an injection wall . the composition comprises an aqueous solution of a welan gum heteropolysaccharide biopolymer produced by the fermentation of a microorganism of the genus alcaligenes , a phenolic compound , an aldehyde and water . the compositions of this invention will form stable gels even in low salinity brines . also provided is a process for selectively plugging regions of higher permeability within an oil - bearing subterranean formation to improve sweep efficiency during a fluid flood oil recovery process using the gel - forming compositions of this invention .