The pr.esent paper deals with a model for obtaining the optimum performance conitions for the KrF laser. The model is based on the dominantformation, quenching and absorption processes. For a given excitationdensity the analysis predicts the maximum photon density rate thatcan be extracted from the cavity together withthe corresponding optimum argon and crypton densities as a function of the excitationrate and outcoupling. The results of various experimental studies indicatedin the paper are in good agreement with these predictions.The analysis shows that the maximum efficiency that corresponds withthe maximum output defined as the ratio of output power and the ionization energy delivered to argon is about 8%.