On the basis of alloy 800 H and alloy AC-66, materials introduced in the 1960s and the late 1980s, respectively, two new alloys, Cronifer III-TM (alloy III-TM) and Nicrofer 45-TM (alloy 45-TM), were developed to resist high sulfur and carbon-bearing environments. Carburization behaviour was examined in the temperature range 750–1100°C for more than 1000 h in CH4/H2(ac= 0.8). The silicon-containing alloys Cronifer III-TM and Nicrofer 45-TM showed a mass gain similar to or even lower than that of the nickel-base alloy 625. Data on sulfidation resistance up to 650°C obtained in 10% SO2/N2indicated a mass loss of less than 5gm−2after 1000h for all alloys tested (800 H, AC-66, 625, III-TM, 45-TM). At 750°C alloy 800 H suffered breakaway corrosion and alloy 625 severe spallation. Alloys AC-66, III-TM and 45-TM showed superior corrosion resistance. Tests performed in a simulated coal gasification environment (1% H2S, 4% CO, 3% H20, balance H2) showed negligible mass gain for the alloys at 550°C. Results at 650°C remained satisfactory after 1000 h for alloys 800 H, AC-66, III-TM and 45-TM, with weight gains of less than 35 gm-2. Metallographic examination of the alloys, however, indicated local corrosion attack, which was lowest for 45-TM at 550°C and lowest for AC-66 at 650°C. Alloy 800 H showed the worst behaviour at all temperatures. Exposure tests in a simulated waste incineration atmosphere (2.5gm−3HC1, 1.3g−3SO2, 9% O2, balance N2) in the temperature range 550–850°C showed alloy 45-TM to have the best performance over the whole temperature range.