The composition of volatile and solid products of oxidation of hydrogen sulfide and stainless steel in gas mixtures containing H2S, O2, H2O, and CO2 has been determined using mass spectrometry, x-ray diffraction analysis, and scanning electron microscopy. It has been shown that holding an H2S–O2 mixture at 301 K results in prevailing formation of elemental sulfur and iron sulfides in the form of porous hygroscopic crust on the reactor wall surface. Formation of gas-phase sulfur causes self-acceleration of the oxidation of hydrogen sulfide; the resulting water triggers corrosion of the reactor wall. Heating of the resulting sulfur-sulfide crust in O2 medium is accompanied by formation of SO2 and heat release at T > 508 K. After heating of the H2S–CO2 mixture to 615 K, H2 and COS were found in the volatile reactants; no noticeable corrosion of the reactor wall has been detected. It has been established that addition of O2 to the H2S–CO2 mixture and its heating to 673 K leads to formation of ferrous sulfates. The mechanisms of the observed processes are discussed.