With tight regulations on the permissible sulfur content in transportation fuels, the oil and gas industry is mandated to adopt reliable and cost-effective desulfurization and acid gas (H2S and CO2) treatment techniques. At present, the Claus process is used to treat acid gas to recover sulfur, but the hydrogen content in H2S is wasted as low grade steam. A viable method of acid gas treatment is the simultaneous production of valuable syngas (H-2 and CO) and sulfur through the thermal destruction of H2S and CO2. However, the optimum process conditions and blends of H2S and CO2 to increase syngas production are not known. In this paper, a detailed reaction mechanism is developed for the simultaneous decomposition of H2S and CO2 and is validated using different sets of experimental data. The effects of the relative composition of H2S and CO2 in the acid gas and the process conditions on the production of syngas and sulfur during thermolysis are reported. A synergistic effect is observed in the simultaneous decomposition of H2S and CO2, i.e., CO2 decomposition to CO is enhanced in the presence of H2S, and H2S conversion is improved in the presence of CO2. The temporal evolution of unwanted sulfurous compounds (SO2 and COS) are also studied at different residence times and temperatures. The major reactions leading to syngas formation during acid gas decomposition are identified. The developed kinetic model can facilitate the design and optimization of the syngas and sulfur recovery process from acid gas.