A method of injecting oxygen into a melt located within a metallurgical furnace having a heated furnace atmosphere in which oxygen and fuel is injected into 1 or more nozzles having passageways of converging-diverging configuration under choked flow conditions to produce supersonic jet or jets discharged from the passageways. Fuel is injected into internal circumferential locations of the passageways so as to impart a structure to the jets being discharged that have an outer circumferential region containing a mixture of fuel and oxygen and a central region containing essentially oxygen. Such a structured jet upon discharge interacts with the furnace atmosphere to create an outer shear-mixing zone in which the outer circumferential layer mixes with the heated furnace atmosphere and auto-ignites to produce a flame envelope surrounding a supersonic jet of oxygen. The jet of oxygen and flame envelope can be directed against a melt contained within the metallurgical furnace for injection of oxygen into the melt.