disclosed is an improved viscous , aqueous , hydrophilic polymer - containing fluid suitable for injection into porous media such as subterranean petroleum - containing earth formations and an oil recovery method in which the aqueous fluid is injected into the subterranean petroleum - containing formation . the fluid contains an effective amount of an aromatic treating substance , preferrably benzene , toluene , xylene , and low alkyl - substituted benzene or toluene . the improvement resulting from incorporation of this additive in the polymer fluid includes greatly increased resistance to microbial degradation of the polymer , improved screen factor , and improves the injectivity of the fluid .