Experimental results are presented from the combustion of toluene with CO2 and H2S gas in H-2/O-2-N-2 flames at an equivalence ratio of Phi = 3 (Claus condition). The results from the combustion of 100% H2S, H2S/C7H8 and H2S/C7H8/CO2 acid gases are also reported. The results showed a decrease in mole fraction of H2S and simultaneous evolution of SO2 in H2S/H-2/O-2-N-2 flame. In contrast, combustion of H2S/C7H8 acid gas showed faster initial SO2 formation to a maximum mole fraction, but the formed SO2 decomposed further downstream in the reactor. This is in further contrast to that of H2S/C7H8/CO2 acid gas combustion, where CO2 acted as an oxidizer (released atomic oxygen) that furthered SO2 formation. The results also revealed the formation of CH4, C2H2 and CS2 with the addition of toluene. The presence of CO2 enhanced the formation of mercaptans (COS and CS2) and decomposition of formed hydrocarbons in the reactor. These results help to identify conditions under which hydrocarbons and mercaptans (COS and CS2) are formed, and how they can be mitigated during sulfur and energy recovery from acid gases. (C) 2015 Elsevier Ltd. All rights reserved.