Monopoly
In one line. A monopoly is a single dominant seller protected by high barriers to entry. It is a price setter with MR below a downward AR, profit maximising where MR equals MC so that price exceeds MC. Supernormal profit is sustained by barriers, output is restricted and there is a deadweight loss, unless economies of scale make it a natural monopoly. H2 only.
Exam relevance: a core H2 microeconomics theme, firms and market structures recur across essay and case study almost every year, on ETG analysis. Taught the way an economics tutor who wrote the answer keys teaches it.
01What a monopoly is
A monopoly sits at the opposite extreme from perfect competition: one dominant seller, shielded from rivals, with real power over price.
H2 only. This whole topic, costs, economies of scale and market structures, is H2 content. H1 students do not study it, so if you are taking H1 Economics you can skip this page.
A monopoly is a market structure with a single dominant seller of a product that has no close substitutes, protected by high barriers to entry.
Because it supplies the whole market, the monopolist faces the market demand curve directly, which is what gives it the power to set price rather than take it.
02High barriers to entry
A monopoly can only persist because high barriers to entry keep new firms out, so its profit is not competed away.
Barriers include large economies of scale that a new entrant could not match, high sunk and setup costs, legal protections such as patents and licences, control of an essential input, and an established brand. Without these barriers, supernormal profit would attract entry and erode the monopoly. The link between barriers and sustained profit is the load bearing point in most monopoly answers.
03The price setter and MR below AR
Because the monopolist faces a downward sloping demand curve, to sell more it must lower the price on all units, so marginal revenue lies below average revenue.
The demand curve is the firm's average revenue curve. Marginal revenue falls faster and lies below it, because selling an extra unit requires cutting the price on every unit sold. This gap is what lets the profit maximising output sit at a price above marginal cost.
04Profit maximisation and supernormal profit
The monopolist profit maximises like any firm, where MR equals MC, but the result is a price above marginal cost and lasting supernormal profit.
A monopoly produces where MR = MC, reads the price off AR, and so sets P greater than MC. Because P is above AC, it earns supernormal profit, which high barriers to entry sustain into the long run.
Unlike a perfectly competitive firm, whose supernormal profit is competed away by entry, the monopolist keeps its profit because barriers block entry. This is the structural difference that drives every comparison between the two.
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05Allocative inefficiency and deadweight loss
Because the monopolist sets price above marginal cost and restricts output, it is allocatively inefficient, and the lost welfare is a deadweight loss.
At the profit maximising output, price exceeds marginal cost, so units that consumers value more than they cost to make are never produced. Compared with the allocatively efficient output where price equals MC, the monopolist produces less and charges more. The welfare destroyed by this restriction is the deadweight loss, the standard measure of the harm from monopoly power.
06The natural monopoly counter case
Monopoly is not always worse than competition, because where economies of scale are very large a single firm can supply most cheaply.
A natural monopoly arises where economies of scale persist over the whole relevant range of output, so one large firm has lower average cost than several smaller firms could. Splitting it up would raise unit costs. The policy answer is then not to force competition but to regulate the single firm, capping its price near average or marginal cost so consumers gain the scale economies without paying the monopoly price.
07Common misconceptions
Read the price off the demand curve (AR), not off MR or MC; the MR equals MC condition only fixes the output. And monopoly is not automatically bad: where economies of scale are large, a regulated natural monopoly can serve consumers more cheaply than fragmented competition.
08Test yourself
- Explain why a monopolist's marginal revenue lies below its average revenue.
- Using the profit maximising condition, explain why a monopoly sets price above marginal cost.
- Give one situation in which a monopoly may serve consumers more cheaply than competition.
09Questions students ask
A monopoly is a market structure with a single dominant seller protected by high barriers to entry. Because it faces the whole market demand curve, it is a price setter with a downward sloping AR and a marginal revenue curve below it. It profit maximises where MR equals MC, charging a price above marginal cost and earning supernormal profit that high barriers sustain. This is H2 content.
A monopoly profit maximises where MR equals MC, but because its demand curve slopes down the price it charges lies above marginal cost. It produces less than the output where price equals MC, so units that consumers value more than they cost are never made. That lost welfare is a deadweight loss, which is why monopoly is allocatively inefficient relative to perfect competition.
Sometimes. Where economies of scale are large enough that a single firm supplies the whole market at lower average cost than several firms could, the market is a natural monopoly, and fragmenting it would raise costs. A regulated natural monopoly can then serve consumers more cheaply than competition, provided its price is capped near average or marginal cost.