Systems and methods for controlling the composition of a combustion exhaust gas are provided. Exemplary methods include introducing a fuel, an oxidant, and a diluent to a combustion zone and combusting at least a portion of the fuel to produce an exhaust gas comprising water, carbon dioxide, oxygen, and carbon monoxide. The exhaust gas may be expanded to produce mechanical power and an expanded exhaust gas. A concentration of at least one of oxygen and carbon monoxide is determined in at least one of the exhaust gas and the expanded exhaust gas. The method continues by adjusting an amount of at least one of the oxidant and the fuel introduced to the combustion zone based at least in part on the determined concentration of at least one of oxygen and carbon monoxide to produce an exhaust gas containing a combined amount of oxygen and carbon monoxide of less than about 2mol %.