What Is a Monopoly? Market Power and Competition Explained

In a perfectly competitive model, many sellers offer similar products and no single firm can strongly control the market price. A monopoly sits at the other extreme. One supplier serves the market, and buyers cannot easily switch to a close substitute. That does not mean the firm can charge any price it wants, because customers still respond to price, but the seller usually has more market power.

Market definition matters when asking what a monopoly is. A company might be the only bakery on one street but still compete with supermarkets, cafes, and bakeries nearby. Economists therefore ask what product is being sold, what substitutes buyers see as realistic, and what geographic area matters. A monopoly claim can look stronger or weaker depending on how narrowly the market is defined.

Monopolies can arise for different reasons. A company may control a scarce resource, own important intellectual property, benefit from very large economies of scale, or operate in an industry where building a second network would be extremely expensive. Government rules can also create exclusive rights in some cases.

A monopoly is easier to maintain when rivals face barriers to entry. These are obstacles that make it hard or costly for new firms to enter the market. A barrier might be a legal licence, a patent, control of key infrastructure, strong network effects, huge start-up costs, or access to a resource that competitors cannot easily obtain.

Natural monopoly is a term used when one large provider can serve the whole market at lower average cost than several smaller providers because fixed costs are very high. Some utility networks are often discussed this way. In those cases, governments may regulate prices or service standards instead of trying to create many duplicate networks.

Understanding barriers gives a clearer answer to what a monopoly is than simply looking for a large company. A firm can be very large and still face strong competition if customers have good alternatives and new rivals can enter. Market power depends on the choices available around the firm, not only its size.

Compared with a competitive market, a profit-seeking monopoly may restrict output and charge a higher price if doing so increases profit. That can transfer some benefit from consumers to the producer and can also reduce trades that would have happened under more competitive conditions. Economists call the lost gains from those missing trades deadweight loss.

Monopoly can also have more complicated effects. Large firms may have resources for research, infrastructure, or long-term investment. At the same time, weak competitive pressure can reduce the urgency to improve quality or cut costs. The outcome depends on the industry, regulation, technology, and behaviour of the firm.

When you revise this topic, separate three questions: how many effective sellers exist, what alternatives customers have, and how hard entry is for new rivals. Those clues tell you much more than the company name alone.

The best-known historical case is Standard Oil, built by John D. Rockefeller in the second half of the nineteenth century. By buying rivals, negotiating secret discounts from railways and using its size to undercut competitors, the company came to control the large majority of oil refining in the United States. Critics argued that it used this position to squeeze out independent producers and set terms for the whole industry. Journalists such as Ida Tarbell documented its methods in detail, and public pressure grew.

The United States had passed the Sherman Antitrust Act in 1890 to outlaw monopolisation and conspiracies in restraint of trade. In 1911 the Supreme Court ruled that Standard Oil had broken the law and ordered it split into separate companies, several of which became major oil firms in their own right. The case shaped the modern idea of competition policy: governments do not usually punish a firm simply for being big, but they can act when market power is gained or kept through practices that block competition.

Imagine a firm that is the only seller of a product and must charge everyone the same price. At 10 pounds it can sell 10 units a day, earning 100 pounds. To sell an 11th unit it must cut the price to 9 pounds for every customer, earning 99 pounds. The extra unit brings in 9 pounds from the new buyer but costs 10 pounds in lower prices to the existing ten, so the firm's revenue actually falls by 1 pound. Economists call the change in revenue from one more unit marginal revenue, and for a single-price monopolist it sits below the price.

Now suppose each unit costs 4 pounds to make. In a competitive market, firms would keep selling as long as a buyer would pay more than 4 pounds, so the 11th, 12th and later units would be produced. The monopolist stops where producing one more unit adds more to cost than to revenue, which happens at a lower quantity and a higher price. The buyers who would happily have paid 9, 8 or 7 pounds, well above the cost of making the goods, go without. Those missing sales are what economists mean by deadweight loss, seen here as real customers rather than an area on a graph.

Market power can sit on the other side of a market too. A monopsony is a market with one dominant buyer, and the classic example is an employer that hires most of the workers in a town, such as a mine or a large factory in an isolated area. Workers with few alternatives cannot easily move to a rival offering better pay. Just as a monopolist sells less to keep prices high, a monopsonist can hire fewer people to keep wages down, because raising pay to attract one more worker usually means raising it for everyone already employed.

The arithmetic mirrors the monopoly example. Suppose a firm employs 20 people at 400 pounds a week, and to attract a 21st worker it must offer 410 pounds to everyone. The new worker costs 410 pounds plus an extra 10 pounds for each of the 20 existing staff, 610 pounds in all. If that worker would add only 500 pounds of value, the firm stops at 20, even though the worker would gladly accept 410. This is why some economists argue that a carefully set minimum wage can raise pay without cutting jobs where employers hold this kind of power.

A monopoly is a market with one effective seller and no close competitor, usually protected by barriers that make entry difficult. Monopoly can create market power over price and output, but the real effect depends on substitutes, regulation, costs, and the possibility of new competition.