What is the difference between Monopoly vs. Oligopoly?

The monopoly is the market where just one firm is present in the market. There is no nearby substitute good available of what a monopolist produces. A monopoly firm is a price maker since it has full command over market supply. Monopolists can decide either price of goods or quantity in the market. Entry and exit are prohibited for new firms. An example of a monopoly - it is related to services related to a public utility such as electricity, transportation, water, etc.

An oligopoly is a market structure wherein there exist very few large sellers that produce similar but slightly different products .and we find interdependence in the decisions of oligopoly firms. The role of advertising and marketing activities are very important in this market. Examples of oligopoly - it can be found in industries like soft drinks, automobiles, telecommunication, etc.