The action of oxygen that leads to the ultimate deterioration of organic materials tends to occur in a sequence of stages. Four successive stages are described: inception, induction, maximum rate or steady state, and declining rate. Examples of possible chemical processes that could be taking place in each of these proposed stages are cited. For example, an attack on weak links in a polymer might occur in the inception stage. The consumption of inhibitors frequently accounts for an induction stage, whereas a maximum rate or steady state stage should occur when the concentration of a major reactant reaches a maximum or constant level. Finally, a declining rate stage can be expected when the concentration of the principal reactant decreases. See also AATA 15-389.