Perfect competition, monopoly, oligopoly and monopolistic competition: their characteristics and effects on price, output and profit.

What this dot point is asking

WJEC wants you to describe the main market structures (perfect competition, monopoly, oligopoly and monopolistic competition), their characteristics and barriers to entry, and how each affects price, output and profit.

The answer

Perfect competition

Because the firm is a price-taker, it faces a horizontal demand curve at the market price, so average revenue equals marginal revenue equals the price. It maximises profit where MC = MR = price. In the short run it can earn abnormal profit or make a loss, but free entry and exit in the long run competes any abnormal profit away (entry raises supply and lowers price) and eliminates losses (exit raises price), so in long-run equilibrium each firm earns only normal profit and produces at minimum average cost where price equals marginal cost. This delivers productive and allocative efficiency, which is why perfect competition is the efficiency benchmark, even though it is rare in reality.

Monopoly and barriers to entry

Barriers to entry are what allow monopoly (and oligopoly) to persist: economies of scale (a natural monopoly where one large firm has the lowest costs), legal barriers (patents, licences), control of an essential resource, high sunk costs, and strong brands. Monopoly is statically inefficient (price above marginal cost, restricted output, possible X-inefficiency), but may exploit economies of scale to lower costs and use abnormal profit to fund innovation (dynamic efficiency). A monopolist may also engage in price discrimination, examined in the next topic.

Oligopoly and monopolistic competition

Oligopoly is defined by interdependence: because a few large firms dominate (high concentration ratio), each must anticipate rivals' responses, which leads to non-price competition (branding, advertising, loyalty schemes), a tendency to price rigidity (the kinked demand curve idea), and the temptation to collude to act like a monopoly, all developed in the market-behaviour topic. Monopolistic competition combines features of competition and monopoly: product differentiation gives each firm a little price-setting power (a downward-sloping demand curve) and short-run abnormal profit, but low barriers mean entry competes that away, so firms earn only normal profit in the long run, though they produce with some spare capacity (not at minimum average cost).

Examples in context

Example 1. Supermarkets and groceries as an oligopoly. The UK grocery market is dominated by a handful of large chains, a classic oligopoly with high barriers to entry (scale, land, brand). The firms compete heavily on non-price terms (loyalty cards, advertising, store quality) and watch one another's prices closely, illustrating interdependence and non-price competition. Periodic price wars and the close scrutiny of mergers reflect the oligopoly behaviour the theory predicts.

Example 2. Utilities and natural monopoly. Water supply and energy networks are natural monopolies: the huge fixed cost of pipes and grids means a single network has the lowest average cost, so competition would be wasteful. Left unregulated, such a monopoly would restrict output and raise price, so the UK regulates these utilities to limit prices and protect consumers. This shows monopoly arising from economies of scale and why it is regulated rather than broken up, linking structure to intervention.

Try this

Q1. State two characteristics of a perfectly competitive market. [2 marks]

• Cue. Any two of: a very large number of firms (price-takers), a homogeneous product, freedom of entry and exit (no barriers), perfect information.

Q2. Explain why a monopoly can earn abnormal profit in the long run but a firm in perfect competition cannot. [3 marks]

• Cue. A monopoly is protected by high barriers to entry that block new firms, so abnormal profit persists; in perfect competition free entry competes abnormal profit away, leaving only normal profit.