With growing generation of municipal solid wastes, development of sustainable disposal techniques is essential for effective utilization of these resources. While waste-to-energy (WtE) facilities provide energy recovery from these wastes, the low relative value of energy makes it unattractive. Simultaneously, high oxidation environment in these facilities also means losing significantly valuable resources such as metals/mineral in the form of their oxides and forming pollutant flue gases and fly-ash. Alternative pathways in waste-to-energy involve designing variable oxygen staging to effectively limit oxidation to only carbonaceous materials while minimizing high oxidation state products of metals. In such operating conditions, formation of char from the MSW components is thermodynamically favored and effective utilization of this resource in-situ can be valuable to improve the reactor operability. In this study, we investigated the feasibility of utilizing waste gypsum from construction/demolition sector to co-process in WtE process. Thermogravimetric analysis (TGA) with FTIR analysis of evolved gas was utilized to understand the operation conditions for such a co-processing and the formation of evolved gas products such as CO2, CO and SO2. Char formed from pyrolysis of waste tires was investigated to examine its reactions with gypsum. Char was found to be reduced by reacting with the anhydrous gypsum at temperatures beyond 850 °C. These studies also include the effect of oxidation potential of the purge gas on this reaction which was carried out by introducing 4.8% O2 into the TGA purge gas to understand its effect on the reaction of gypsum with the char in comparison to char oxidation.