An Oligopoly is the act of participating in a monopoly with multiple companies. Behind closed doors the companies will usually agree not to compete with each other in certain regions of a country, state, or city. This can lead to the severe spike in prices without the need for compensation due to competition. This act, while royally fucking a consumer, can provide access to a previously illegal business practice with zero negative repercussions and an immunity to any legal action being taken against the companies in question.
Comcast : So Time Warner, You take New York, I'll take California, and AT&T can take Texas.
Verizon : This is looking to be the most corrupt Oligopoly to date!