The report gives results of investigations of four ways to control nitrogen oxide (NOx) emissions from package boilers (both field operating boilers and boiler simulators): (1) variations in combustor operating procedure; (2) combustion modification (flue gas recirculation and staged combustion); (3) use of an alternate fuel, methanol; and (4) burner design optimization. Comparative tests were conducted in a firetube boiler. Reduced excess-air firing was the only NOx control that both reduced emissions and increased thermal efficiency. Flue gas recirculation and staged combustion had negligible effects on boiler operating efficiency. Conversion to methanol results in a considerable decrease in thermal efficiency because of the water vapor's increasing the enthalpy of the flue gas.