In the nonpremix furnace firing strategy FODI (Fuel/Oxidant Direct Injection), fuel and oxidant jets discharge directly into the furnace cavity rather than into a burner quarl. The jets entrain substantial quantities of product gases that have cooled by furnace heat transfer. Thus fuel and oxidant enter the subsequent combustion zone much diluted by cooled products, depressing reaction temperatures and reactant concentrations and so greatly reducing NOx emissions. In the present realization, FODI is implemented in a patented unitary burner providing a plurality of oxidant jets surrounded by a plurality of fuel jets, suitable for retrofit as well as new installations and particularly advantageous for applications with air preheat. We here present results of experimental investigation and theoretical analysis of the burner performance. Characteristic of FODI, NOx reduction is won at an expense to combustion stability, confining steady-state operation to furnace refractory temperatures above about 870 degrees C and exhaust gas temperatures above about 1000 degrees C. The NOx emissions vary strongly with the temperature of the recirculating furnace gases; when the furnace load is substantial, that temperature falls much below the adiabatic combustion level and NOx is very low. By appropriate choice of burner design parameters, reasonably small combustion zones are obtained, avoiding wall impingement and enhancing stability. The analysis given of burner behavior, particularly in respect to combustion aerodynamics, is revealing in respect to mechanisms and provides a basis for assessing effects of variations in design, including scaleup. The present is the first systematic investigation of a system employing FODI, and the general analysis is pertinent to other FODI implementations. This is a new and challenging field for combustion research, involving complex mixing processes coupled with nonadiabatic reaction at unusually low temperatures and concentrations. Much work remains to be done on the detailed mechanisms of mixing and reaction and on the development of appropriate mathematical modeling.