  We analyze the origin of ferromagnetism as a result of carrier mediation in
diluted magnetic oxide semiconductors in the light of the experimental evidence
reported in the literature. We propose that a combination of percolation of
magnetic polarons at lower temperature and Ruderman-Kittel-Kasuya-Yosida
ferromagnetism at higher temperature may be the reason for the very high
critical temperatures measured (up to ~700 K).
