A solution of an oxygenated polyamine, which is the reaction product of dimethylamine and epichlorohydrin, has been discovered to possess excellent stabilization properties when used as a treatment for stabilizing a clay containing formation, for example in the treatment of oil and gas producing boreholes which penetrate clay containing formations. Preferred copolymers of this type which are useful in clay formation treatments include those having epichlorohydrin to dimethylamine mole ratios in the range of from about 0.79 to about 0.93.