A method of minimizing the production of SO.sub.x and NO.sub.x in the burning of a fuel containing significant amounts of SO.sub.x and NO.sub.x precursors in which the fuel is treated to remove significant amounts of SO.sub.x precursors without the removal of significant amounts of NO.sub.x precursors and the fuel is thereafter burned in a two-stage, rich-lean burning step in which significant amounts of the NO.sub.x precursors are converted to N.sub.2. Treating the fuel to remove SO.sub.x precursors is preferrably carried out in the presence of an oxidizing agent, such as H.sub.2 O.sub.2, a reducing agent, such as hydrogen, and/or steam, and still more preferably, the oxidizing agent, the reducing agent and steam are generated by burning an auxiliary fuel and passing the effluent thereof to the step of treating the fuel to remove SO.sub.x precursors.