Final answer:
Oligopolies exist due to a combination of barriers to entry that create monopolies and product differentiation. Some entry barriers in oligopolistic markets include control of a physical resource, legal restrictions, patent protection, and economies of scale. Intellectual property laws also contribute to entry barriers.
Step-by-step explanation:
An oligopoly is a market structure characterized by very few producers supplying similar products with high barriers to entry. Some of the entry barriers present in oligopolistic markets include: control of a physical resource, legal restrictions on competition, patent protection, and practices like predatory pricing. Intellectual property laws such as patents, copyrights, trademarks, and trade secrets also contribute to entry barriers. Additionally, economies of scale and market demand can create barriers to entry in oligopoly markets.