What is a monopoly?
A monopoly is an enterprise that is the only seller of a good service. In the absence of government intervention, a monopoly is free to set any price it chooses and will usually set the price that yields the largest possible profit. (Stigler, 2013)
What is an Oligopoly?
Oligopoly is an industry can only have a handful of large firms; it makes it very difficult for new firms to enter into the industry. The firm products can be similar or different, but the action of one firm will impact others in the oligopoly. (Wessels, 2000)

What is a Cartel?
A Cartel is a group of firms in an oligopoly that get together and agree to cooperate to the detriment of consumers and other firms. The benefit of cooperation is that the oligopolists can charge higher prices to consumer end up with less than they otherwise might have consumed. (Wessels, 2000) Example of a Monopoly:
Examples of monopolies includes Microsoft and Windows, DeBeers and diamond, your local natural gas company. Individual restaurants and other products that enjoy brand loyalty in otherwise competitive markets will choose prices and output just like monopolists do. (Monopoly)
Phone companies are an example of the breakup of a firm with monopoly power. AT&T was forced to break into a number of local phone companies back in 1982, with several regional operating companies such as bell south etc. Today, AT&T and Verizon control most of the market and dominate the declining fixed line business as well as the growing mobile phone space. Industry dynamics have changed greatly since the breakup of the original AT&T and the internet could continue to force it to evolve. (Investopedia, 2011) Example of an Oligopoly:
Smartphone’s operating systems is an example of oligopolies; the