  Concentration phenomena concern the ICT market. Though the regulatory action
has been active mainly in the telecom network operators industry, even more
significant worldwide concentration phenomena affect other industries. The
market of mobile operating systems is analysed through two concentration
indices to get a quantitative picture of the current situation and its
evolution over time: the Hirschman Herfindahl Index (HHI) and the Four-Firm
Concentration Ratio (CR4). A strongly imbalanced oligopoly is shown to exist,
where the four major operating systems take over 99% of the market, but the
dominant operating system Android alone is installed on over 80% of the new
devices.
