Natural Monopoly
What is Natural Monopoly?
A natural monopoly occurs when a single firm can produce the entire market output at a lower average total cost than multiple firms could.
This typically happens in industries with very high fixed costs and low marginal costs, such as utilities, where economies of scale are so large that one firm is more efficient than many. Government regulation is often used to prevent abuse of market power.
Natural Monopoly: a worked example
Suppose laying a town's water pipe network costs $9,000,000 no matter how much water flows, and pumping each thousand gallons costs $1. One firm serving 3,000,000 units has total cost 9,000,000 + 3,000,000 = $12,000,000, so average total cost is 12,000,000 / 3,000,000 = $4. Now let two firms each build their own network and split the market at 1,500,000 units apiece. Each has total cost 9,000,000 + 1,500,000 = $10,500,000, giving average total cost of 10,500,000 / 1,500,000 = $7. Competition raised the cost per unit from $4 to $7, because the $9,000,000 pipe bill got paid twice.
The mistake students make with natural monopoly
Students hear natural monopoly and picture a firm that owns a natural resource, like the only lithium deposit in a country. The word natural describes the cost structure, not the product: average total cost keeps falling across the entire range of market demand, so one firm serves everyone more cheaply than two could. A resource monopoly is a separate barrier to entry. A second slip is assuming regulators can simply set price equal to marginal cost, which forces a loss whenever ATC is still falling.
Natural Monopoly questions
Why does a natural monopoly have falling average total cost?
A natural monopoly has falling average total cost because an enormous fixed cost gets spread across more and more units while the cost of serving one extra customer stays small. Each new unit pulls the average down toward marginal cost without ever reaching it. Since demand runs out before the average total cost curve stops falling, the firm never exhausts its economies of scale.
Why is a natural monopoly regulated instead of broken into smaller firms?
A natural monopoly is regulated rather than broken up because splitting it forces every new firm to duplicate the same huge fixed cost. Two sets of pipes or two parallel rail lines cost roughly twice as much to build and each serves half the customers, so average total cost rises for everyone. Regulating the single low-cost producer's price keeps the cost advantage while limiting the markup.
What is the difference between socially optimal and fair return pricing?
Socially optimal pricing for a regulated natural monopoly sets price equal to marginal cost, while fair return pricing sets price equal to average total cost. Because average total cost is still falling, marginal cost lies below it, so the socially optimal price leaves the firm with a loss that needs a subsidy. The fair return price is higher and gives the firm zero economic profit.
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