The corrosion behavior of pure Mo and three Mo-Al alloys containing 28, 50, and 75 atom % Al was studied over the temperature range of 800-100 degrees C in a H-2/H2S/H2O gas mixture. Except for the Mo-50Al alloy consisting of a two-phase structure of Mo3Al and Mo(3)AI(8), other alloys studied were single phase. The corrosion kinetics followed the parabolic rate law in all cases, regardless of temperature and alloy composition. The parabolic rate constants increased with increasing temperature but decreased with increasing Al content. The Mo-75Al alloy exhibited the best corrosion resistance among all alloys studied, whose corrosion rates are 2.1-3.0 orders of magnitude lower than those of pure Mo (depending on temperature). A layer exclusively of MoS2 formed on pure Mo, while heterophasic scales were observed on Mo-Al alloys. The scales formed on Mo-28Al consisted of alpha-Al2O3 and MoS2 at T less than or equal to 900 degrees C and of alpha-Al2O3, MoS2, and Al0.55Mo2S4 at 1000 degrees C, while the scales formed on Mo-50Al consisted of mostly alpha-Al2O3, and a minor amount of MoS2. The scales formed on Mo-75Al consisted exclusively of alpha-Al2O3, at T 900 degrees C and of mostly alpha-Al2O3 and a minor amount of MoS2 at 1000 degrees C. The formation of alpha-Al2O3 is responsible for the significant reduction of the corrosion rates as compared with those of pure Mo.