In a glass melting furnace of the type that has a basin wherein a bath of molten glass is heated by a blanket of flame that extends over the molten bath, performance and productivity are enhanced by installing oxygen injection lances through holes that are drilled through walls of the furnace at tuck stone levels just above the top surface of the molten bath of glass in the furnace basin. The lances are thin walled tubes that each carry an adjustable flange for preventing unwanted convection and radiation through furnace wall holes that receive the lances. By bending the thin walled tubes to carefully direct the discharging flows of oxygen so that the discharge paths properly extend across the top surface of the molten bath in closely spaced, parallel relationship thereto, and by selecting discharge opening sizes, the injected flows of oxygen are aimed and defined so as to effectively draw the blanket of flame down to surface portions of the molten material that is being heated, and to achieve complete combustion and maximum flame coverage. Thus both flame positioning and combustion efficiency are improved concurrently.