Abstract: Cobalt base alloys for use at elevated temperatures are disclosed that possess excellent resistance to oxidation/corrosion at elevated temperatures in combination with mechanical properties which exceed those of similar alloys currently in use. The resistance to oxidation/corrosion is afforded by a particular combination of aluminum and chromium which act to form a protective alumina layer and a synergistic combination of hafnium and yttrium which act to promote adherence of the alumina. Refractory metal additions are utilized to improve the mechanical properties. The alloys of the invention are suited for use in gas turbine engines as well as industrial applications such as furnaces and chemical process apparatus.