One measure that shows if an oligopoly is present is the concentration ratio, which calculates the size of companies in comparison to their industry. Instances where a high concentration ratio is present include mass media. In the U.S., for example, the sector is dominated by just five companies: NBC Universal; Walt Disney; Time Warner; Viacom CBS; and News Corporation—even as streaming services like Netflix and Amazon Prime begin to encroach on this market. Meanwhile, within big tech, two companies control smartphone operating systems: Google Android and Apple iOS.