Apparatus is described for combusting exhaust gases output from a plurality of process chambers. The apparatus comprises a plurality of exhaust gas combustion nozzles (22) connected to a combustion chamber (24). Each nozzle receives a respective exhaust gas (26), and comprises means for receiving a fuel (40) and an oxidant (30) for use in forming a combustion flame within the chamber. A controller receives data indicative of the chemistry of the exhaust gas supplied to each nozzle, and adjusts the relative amounts of fuel and oxidant supplied to each nozzle in response to the received data. This can enable the nature of each combustion flame to be selectively modified according to the nature of the exhaust gases to be destroyed by that flame, thereby enhancing the destruction rate efficiency of the exhaust gas and optimising fuel consumption.