A gas turbine combustion system is provided comprising a combustion chamber (16) having a central axis (44), a primary combustion stage (28) located at a front end (32) of the combustion chamber (16) for injecting fuel, air, or mixtures thereof substantially along the central axis (44), a plurality of secondary combustion stages (30A-D) spaced apart in flow series along a length of the combustion chamber (16), wherein each of the plurality of secondary combustion stages (30A-D) comprises a plurality of circumferentially-spaced secondary injectors (48) for injecting fuel, air, or mixtures thereof, toward the central axis (44), and wherein an internal diameter of the combustion chamber (16) decreases from at least a first one of the plurality of secondary combustion stages (30AD) to at least a second one of the plurality of secondary combustion stages (30A-D).