Investigations on the effect of acid gas (H2S and CO2) addition in hydrogen/air flame are presented. The specific equivalence ratios examined include Claus conditions (Phi = 3.0) as well as stoichiometric conditions (Phi = 1.0) and fuel-lean conditions (Phi = 0.5). Two different acid gas compositions of 100% H2S, and 50% H2S/50% CO2 are reported. Addition of pure hydrogen sulfide acid gas deteriorated the rate of hydrogen oxidation in the hydrogen/air flame. Combustion of hydrogen sulfide alone formed sulfur dioxide rather than more favorable elemental sulfur. In contrast combustion of 50% H2S/50% CO2 acid gas stream produced faster decomposition/production of H2S, SO2, and H-2. Presence of carbon monoxide was a distinct mark on the release of oxygen from CO2 into the reaction pool. The presence of carbon monoxide triggered the formation of other sulfurous-carbonaceous compounds, such as COS and CS2. (C) 2013 Elsevier Ltd. All rights reserved.