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For the use of a gas aggregation cluster source a high and stable deposition rate is desired. For many metals, nanoparticle formation is enhanced by admixture of reactive gases. Here, the role of reactive gas admixtures on the nanoparticle deposition rates is investigated for the case of reactive direct current magnetron sputtering of Ti in a gas aggregation chamber. The results show that, at low working gas (argon) pressures, stable cluster deposition at high rates can only be achieved for admixtures with a very narrow oxygen flow range. At higher pressures, stable deposition can be observed only after an intermediate maximum rate has been crossed or a stable deposition rate is not reached at all. For the different sputtering conditions, the partial pressure of oxygen was monitored with a mass spectrometer. The results are explained in terms of the competing roles of oxygen in cluster nucleation as well as in target poisoning. The cluster size distributions for different conditions were characterized by scanning electron microscopy. [ABSTRACT FROM AUTHOR]