Stukenberg and McKinney have drawn an interesting comparison between air activated sludge and oxygen activated sludge systems.1 Their paper examines the “two prominently claimed benefits of oxygen…1) better effluent quality than obtained from conventionally aerated activated sludge systems, generally with a shorter detention time, and 2) less waste activated sludge than produced by a conventionally aerated system.” The second claim is made repeatedly by manufacturers of the oxygen activated sludge systems and has often been contested in the technical literature. The first claim with its emphasis on effluent quality is not as widely stated by oxygen activated sludge advocates. True, manufacturers of oxygen activated sludge systems claim that smaller tanks can be used. However, the superiority of effluent quality is not as commonly claimed by oxygen advocates. In fact, a representative of the Union Carbide Corporation (UCC), the largest commercial supplier of oxygen systems, states that “we would not produce any worse or any better effluent quality than a well designed, well operated municipal air activated sludge system…”2 An identical statement has been made by a representative of UCC’s leading competitor, Air Products and Chemicals.3 Thus, there seems to be at least a degree of agreement on the issue of effluent quality.