A method of introducing oxygen into a boiler system for combustion with a prepared fuel in a furnace combustion chamber comprises providing a plurality of swirl-inducing elements to the air stream delivery lines, and a plurality of oxygen delivery jets adjacent the intake region and substantially surrounding the air stream delivery lines; igniting the fuel gas to create a flame; and delivering a stream of oxygen through the jets tangentially to the flame envelope to substantially shape and stabilize a swirling flow field for the flame, the oxygen concentration in the flame envelope gradually increasing towards an outer periphery of the flame envelope. A boiler system for using the method can be a new system or a retrofit to an existing system. The method and system provide advantages in reduced environmental impact and increased efficiency while addressing the safety factors involved in introducing oxygen to boiler systems.