Abstract: A method of automatically controlling the addition rate of Fresh Oxygen Scavenger Product and Ultimate Oxygen Scavenger Product to a Boiler System is described and claimed. The method is based on the inherent fluorometric properties of certain Fresh Oxygen Scavenger Products and certain Ultimate Oxygen Scavengers in their reduced (unreacted) form and also, for the Ultimate Oxygen Scavengers, in their oxidized (reacted) form. It has also been found possible to enhance the fluorescent signal of certain Oxygen Scavengers by adding a borate buffer to the sample stream. By using the method of the instant claimed invention it is now possible to improve the overall control of Boiler Systems using certain Fresh Oxygen Scavenger Products and certain Ultimate Oxygen Scavenger Products.