This report reviews chemical reactions leading to the formation of ammonia in Hanford wastes. The general features of the chemistry of the organic compounds in the Hanford wastes are briefly outlined. The radiolytic and thermal free radical reactions that are responsible for the initiation and propagation of the oxidative degradation reactions of the nitrogen-containing complexants, trisodium HEDTA and tetrasodium EDTA, are outlined. In addition, the roles played by three different ionic reaction pathways for the oxidation of the same compounds and their degradation products are described as a prelude to the discussion of the formation of ammonia. The reaction pathways postulated for its formation are based on tank observations, laboratory studies with simulated and actual wastes, and the review of the scientific literature. Ammonia derives from the reduction of nitrite ion (most important), from the conversion of organic nitrogen in the complexants and their degradation products, and from radiolytic reactions of nitrous oxide and nitrogen (least important).Reduction of nitrite ions is believed to be the most important source of ammonia. Whether by radiolytic or thermal routes, nitrite reduction reactions proceed through nitrogen dioxide, nitric oxide, the nitrosyl anion, and the hyponitrite anion. Nitrite ion is also converted into hydroxylamine, another important intermediate on the pathway to form ammonia. These reaction pathways additionally result in the formation of nitrous oxide and molecular nitrogen, whereas hydrogen formation is produced in a separate reaction sequence.The oxidative degradation of trisodium EDTA and tetrasodium HEDTA also yields ammonia and other nitrogenous gases. The complexants react with nitric oxide and nitrogen dioxide to produce oxidized compounds that subsequently undergo hydrolysis, eventually liberating ammonia. Amides and nitriles are intermediates in these long reaction sequences. , The direct reaction of hydrogen with nitrous oxide and nitrogen can account for only negligible quantities of ammonia in Hanford tanks. Thermal reactions require high temperatures (AOOOC), high pressures, and the presence of catalysts, to proceed at significant rates. Similarly, radiolytic yields for direct reactions of hydrogen with nitrogen and nitrous oxide under tank conditions are expected to be very small.Oxygen can substantially alter the yields of nitrogenous gases. Two principal pathways have been identified. Oxygen intercepts radicals produced in thermal and radiolytic reactions that would otherwise eventually result in the formation of nitrogen, nitrous oxide and ammonia. Oxygen also reacts directly with complexants and intermediates to yield oxalate ion. The hydrogen yield is often increased in the presence of oxygen.