The understanding of the kinetics leading to the formation of gaseous sulfur species is of great importance because of their corrosive nature in coal-fired energy systems. In this study, reaction kinetics of important gaseous sulfur species in coal combustion are investigated using a detailed reaction mechanism with 10 sulfur species and 49 sulfur-related elementary reactions in combination with GRI-Mech 2.11 for hydrocarbon related reactions and a global two-step reaction mechanism for coal devolatilization and char oxidation. The reaction mechanism was applied to numerical simulations of an entrained-flow reactor, where lignite was burned with varying air ratio. The results of numerical simulations showed that H2S released during devolatilization is fast oxidized and is formed again under reducing conditions as coal conversion proceeds. Calculated concentrations of CO2, CO, and H2S show very good agreement with experimental data. SO2 concentrations under sub-stoichiometric conditions are overpredicted, most likely because not all sulfur is released or because part of the sulfur is bound by minerals in the fly ash in the experiments, which is not taken into account by the simulations.