Another reason for the barriers against entry into a monopolistic industryis that oftentimes, one entity has the exclusive rights to a natural resource. For example, in Saudi Arabia the government has sole control over the oil industry. A monopoly may also form when a company has a copyright or patent that prevents others from entering the market. Pfizer, for instance, had a patent on Viagra. in an oligopoly, there are only a few firms that make up an industry. This select group of firms has control over the price and. like a monopoly. an oligopoly has high barriers to entry. The products that the oligopolistic firms produce are often nearly identical and, therefore, the companies, which are competing for market share, are interdependent as a result of market forces. Assume, for example, that an economy needs only 100 widgets. Company x produces so widgets and its competitor. Company Y produces the other 50. The prices of the two brands will be interdependent and, therefore, similar. So. if Company X starts selling the widgets at a lower price. it will get a greater market share, thereby forcing Company Y to lower its prices as well.