Barium sulfate scale occurrence is a severe production problem in North Sea oil operations. Barium sulfate is often accompanied by strontium sulfate to form a completely mixed scale called (Ba, Sr)SO4 solid solution. This paper describes a laboratory study carried out at 70°C to examine (Ba, Sr)SO4 solid-solution scale formation in porous media and the formation damage resulting from the mixing of two incompatible waters. The paper is a continuation of the previously reported room-temperature work. Results of experiments carried out at the elevated temperatures again demonstrate that substantial scale deposition can occur in a rock core and can cause considerable decline of rock permeability as a result of concurrent flowing of two incompatible waters.