The report gives information necessary for development and generalization of low-NOx oil burner technology for package firetube boilers. It gives results of experiments at two scales: 20 kW and 1.08 MW heat input. At 20 kW, effects of fuel properties were examined in tests of 3 distillate oils, 13 petroleum-derived residual fuel oils, 3 alternate liquid fuels, and 14 doped and/or blended liquid fuels. The tests included systematic variation of excess air and drop size distribution, normal and staged combustion conditions, and separation of fuel NOx from total NOx. At 1.08 MW, experiments concentrated on the interaction between spray characteristics and the combustion aerodynamic flowfield. Spray characteristics were varied by using different commercial atomizing nozzles and by adjusting nozzle operating conditions. Combustion flowfield was varied by modifying the swirl level on the combustion air.