Natural monopoly

Some markets are cheapest to serve with a single firm. Forcing competition into them would waste resources, which is the puzzle of natural monopoly.

A natural monopoly is a market in which a single firm can supply the entire demand at a lower cost than two or more firms could, because of very large economies of scale relative to the size of the market. In such cases, monopoly is not an aberration to be broken up but the efficient structure, which poses a distinctive policy problem.

When one firm is cheapest

A natural monopoly arises where the fixed costs of providing a service are enormous and the marginal costs of serving each additional customer are low, so that average cost keeps falling as output rises across the whole market. Networks, water, electricity, gas, railways, telecommunications infrastructure, are the classic examples: building a second set of pipes, cables, or tracks alongside the first would duplicate vast fixed costs for no gain. One firm spreading the huge fixed cost over all customers can supply more cheaply than several could, so competition would actually raise costs.

The policy dilemma

Natural monopoly creates a genuine dilemma. Competition is undesirable, because it would waste resources duplicating costly infrastructure, yet an unregulated monopoly would exploit its position, charging high prices and restricting output. Society thus cannot rely on either competition or a free monopoly to deliver good outcomes. The result is that natural monopolies are typically either publicly owned or privately owned but regulated, with prices and conditions overseen by the state to capture the efficiency of single supply while preventing the abuse of monopoly power.

Changing boundaries

What counts as a natural monopoly is not fixed; it shifts with technology and market size. Parts of an industry once thought naturally monopolistic can become competitive as technology changes, which is why many utilities have been restructured to separate the genuinely monopolistic network, the wires or pipes, kept regulated, from the potentially competitive activities, generation or retail supply, opened to competition. The art of regulation is identifying which parts are truly natural monopolies and which can bear competition.

Natural monopoly is the case where the usual prescription of competition fails, because a single firm is genuinely the efficient supplier. It explains why some essential industries are monopolies by design rather than by abuse, and why their regulation, balancing the efficiency of single supply against the dangers of unchecked monopoly power, is one of the enduring challenges of economic policy.