The metal dusting behavior of several nickel based alloys was investigated in a gaseous environment composed of 49% CO-49% H2-2% H2O having a carbon activity of 18.9. Samples of the alloys were exposed in the test environment at a temperature of 650°C for periods up to 10,000 hours. Periodically, the samples were removed from test to determine metal wastage and to examine them for pitting attack. The materials tested included alloys that form chromia, alumina and silica type scales. Results of the exposures are interpreted in terms of the compositional variations of the alloys tested.