Hydrogen sulfide oxidation experiments were conducted in O2/N2 at high pressure (30 and 100 bar) under oxidizing and stoichiometric conditions. Temperatures ranged from 450 to 925 K, with residence times of 3–20 s. Under stoichiometric conditions, the oxidation of H2S was initiated at 600 K and almost completed at 900 K. Under oxidizing conditions, the onset temperature for reaction was 500–550 K, depending on pressure and residence time, with full oxidization to SO2 at 550–600 K. Similar results were obtained in quartz and alumina tubes, indicating little influence of surface chemistry. The data were interpreted in terms of a detailed chemical kinetic model. The rate constants for selected reactions, including SH + O2 ⇄ SO2 + H, were determined from ab initio calculations. Modeling predictions generally overpredicted the temperature for onset of reaction. Calculations were sensitive to reactions of the comparatively unreactive SH radical. Under stoichiometric conditions, the oxidation rate was mostly controlled by the SH + SH branching ratio to form H2S + S (promoting reaction) and HSSH (terminating). Further work is desirable on the SH + SH recombination and on subsequent reactions in the S2 subset of the mechanism. Under oxidizing conditions, a high O2 concentration (augmented by the high pressure) causes the termolecular reaction SH + O2 + O2 → HSO + O3 to become the major consumption step for SH, according to the model. Consequently, calculations become very sensitive to the rate constant and product channels for the H2S + O3 reaction, which are currently not well established.