We investigated the potential of optical emission spectroscopy (OES) for accurate control of deposition rate during the deposition of X-ray multilayer mirrors by a radio-frequency magnetron lron sputtrrine technique. The behavior of sputtered atom line intensities versus the argon buffer gas pressure and the r.f. power was investigated and compared to the behavior of the self-bias voltage V-sb, of the sputtered target versus discharge parameters. For an usual working pressure p(Ar) = 2 mTorr and tungsten target, the spectral line intensity I, of sputtered atoms increases with the r.f. power p(r.f.), as I-W alpha P-r.f.(2.2) while V-sb alpha P-r.f.(0.6). Deposition rate has been found to increase almost quadratically with the power (R-D alpha P-r.f.(2)). I-W was found to be relatively insensitive to pressure changes in the 2-10 mTTorr range regardless of the level of the r.f. power used (100-400 W) while V-sb shows a strong pressure dependence.