The goal of this paper is to present a new control method of reactive magnetron sputtering. The processes of reactive magnetron sputtering of aluminum target in Ar + O-2 atmosphere in high efficiency deposition and low efficiency deposition mode were studied. The mode of magnetron operation - metallic, transient, reactive (compound) - was determined by the analysis of medium frequency (MF) magnetron voltage and current waveforms and a circulating power (power supply parameter). This parameter enables monitoring of any mismatch between plasma-magnetron impedance and the resonant circuit of power supply. The experiments show that the AlxOy layer formation conditions could be determined by use of the power supply parameters. Conclusions were supported by the refractive index and dielectric constant measurements. (C) 2011 Elsevier B.V. All rights reserved.