The behaviour of , the saturation intensity averaged over the optical cavity width w of a transverse-flow laser, is discussed based on a numerical analysis of a laser of that type. It is shown that for any w the mean saturation intensity is almost independent of the cavity position x along the flow and remains nearly unaffected by the optical power extraction upstream of the cavity. Thus, similarly as for non-flow lasers, it can be used, in conjunction with the small-signal gain coefficient averaged over the cavity width, for prediction of the optical power available from a transverse-flow laser and optimization of the optical cavity position and width. For axial-flow lasers the available optical power can be predicted in the same way if the beam path along the discharge is taken for w.