A loaded-gain model of a CW flowing oxygen-iodine medium is described, and its principal assumptions and approximations are discussed. The model includes pumping of the upper laser level by O(2)(1 Delta), deactivation losses by water, and stimulated emission. The solution of the model in the absence of flux is obtained, from which a small-signal gain is determined. The model is solved for the output power from a Fabry-Perot resonator as a function of the medium and resonator parameters. It is shown that the maximum available power from the medium is determined by the O(2)(1 Delta) concentration at the nozzle exit plane.© (1990) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.