In monopolistic competitionmonopolistic competitionMarket in which many sellers supply differentiated products., we still have many sellers (as we had under perfect competition). Now, however, they don’t sell identical products. Instead, they sell differentiated products—products that differ somewhat, or are perceived to differ, even though they serve a similar purpose. Products can be differentiated in a number of ways, including quality, style, convenience, location, and brand name. Some people prefer Coke over Pepsi, even though the two products are quite similar. But what if there was a substantial price difference between the two? In that case, buyers could be persuaded to switch from one to the other. Thus, if Coke has a big promotional sale at a supermarket chain, some Pepsi drinkers might switch (at least temporarily).

How is product differentiation accomplished? Sometimes, it’s simply geographical; you probably buy gasoline at the station closest to your home regardless of the brand. At other times, perceived differences between products are promoted by advertising designed to convince consumers that one product is different from another—and better than it. Regardless of customer loyalty to a product, however, if its price goes too high, the seller will lose business to a competitor. Under monopolistic competition, therefore, companies have only limited control over price.

OligopolyoligopolyMarket in which a few sellers supply a large portion of all the products sold in the marketplace. means few sellers. In an oligopolistic market, each seller supplies a large portion of all the products sold in the marketplace. In addition, because the cost of starting a business in an oligopolistic industry is usually high, the number of firms entering it is low.

Companies in oligopolistic industries include such large-scale enterprises as automobile companies and airlines. As large firms supplying a sizable portion of a market, these companies have some control over the prices they charge. But there’s a catch: because products are fairly similar, when one company lowers prices, others are often forced to follow suit to remain competitive. You see this practice all the time in the airline industry: When American Airlines announces a fare decrease, Continental, United Airlines, and others do likewise. When one automaker offers a special deal, its competitors usually come up with similar promotions.

In terms of the number of sellers and degree of competition, monopolies lie at the opposite end of the spectrum from perfect competition. In perfect competition, there are many small companies, none of which can control prices; they simply accept the market price determined by supply and demand. In a monopolymonopolyMarket in which there is only one seller supplying products at regulated prices., however, there’s only one seller in the market. The market could be a geographical area, such as a city or a regional area, and doesn’t necessarily have to be an entire country.

There are few monopolies in the United States because the government limits them. Most fall into one of two categories: natural and legal. Natural monopoliesnatural monopolyMonopoly in which, because of the industry’s importance to society, one seller is permitted to supply products without competition. include public utilities, such as electricity and gas suppliers. Such enterprises require huge investments, and it would be inefficient to duplicate the products that they provide. They inhibit competition, but they’re legal because they’re important to society. In exchange for the right to conduct business without competition, they’re regulated. For instance, they can’t charge whatever prices they want, but they must adhere to government-controlled prices. As a rule, they’re required to serve all customers, even if doing so isn’t cost efficient.