There is an increasing need for, and an increasing demand for, the reduction of stream pollution. In connection with biological wastes and some types of chemical wastes, dissolved oxygen is one of the resources which is needed in the process of stream self-purification. The transport or diffusion of dissolved oxygen in the thin region or film immediately below the water surface is the most critical region in determining the oxygen absorption rate. The surface film is actually an oxygen boundary layer. It should be expected that the film or boundary layer thickness changes with Schmidt number as well as mixing conditions and that the transport through the film can be represented by a diffusion model, as in other boundary layer problems. Using the boundary layer and diffusion model, analytical solutions are presented for the vertical concentration distribution both in the turbulent film and below the film for various situations involving no oxygen demand, sulfite, or BOD. The solutions substantiate that the concentration distribution is essentially linear in the film.