How does the level of competition affect price and output?
Compare the characteristics and outcomes of perfect competition, monopoly, oligopoly and monopolistic competition.
The four main market structures, their features, and how competition shapes price, output, efficiency and the role of the ACCC in Australia.
Reviewed by: AI editorial process; not yet individually human-reviewed
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What this dot point is asking
Market structure describes the competitive environment a firm operates in. The key features that distinguish structures are: the number of firms, the type of product (identical or differentiated), barriers to entry and exit, and the degree of market power or price-setting ability.
Perfect competition
Perfect competition has many small firms selling an identical product, with no barriers to entry and perfect information. Each firm is a price taker, facing a horizontal demand curve at the market price. Firms can earn supernormal profit in the short run, but free entry competes profit away so that in the long run firms earn only normal profit, producing where price equals marginal cost. This delivers both allocative efficiency (price equals marginal cost) and productive efficiency (production at lowest average cost). Few real markets are perfectly competitive, though some agricultural and currency markets come close.
Monopoly
A monopoly is a single seller of a product with no close substitutes, protected by high barriers to entry such as legal patents, control of a resource, or large economies of scale (a natural monopoly). The monopolist is a price maker and faces the whole downward-sloping market demand curve. It maximises profit where marginal revenue equals marginal cost, then charges the higher price the demand curve allows. The result is higher prices and lower output than under competition, causing allocative inefficiency and deadweight loss, and supernormal profit can persist in the long run because entry is blocked.
Oligopoly
An oligopoly is a market dominated by a few large firms, often with high barriers to entry and interdependence, meaning each firm must consider rivals' reactions. Australian examples include the supermarket sector (Woolworths and Coles) and the major banks. Firms may compete through non-price methods like advertising and loyalty programs, and prices can be sticky. There is a risk of collusion, where firms act together like a monopoly to fix prices, which is illegal under Australian law.
Monopolistic competition
Monopolistic competition has many firms selling differentiated products with low barriers to entry, for example cafes, hairdressers and clothing retailers. Product differentiation gives each firm a little market power and a downward-sloping demand curve, so it can set price slightly above marginal cost. Free entry erodes profit to normal levels in the long run, but the outcome is not fully efficient because firms operate with some spare capacity.
Competition policy in Australia
Because market power can harm consumers, the Australian Competition and Consumer Commission (ACCC) enforces the Competition and Consumer Act. It blocks anti-competitive mergers, prosecutes cartels and price-fixing, and regulates natural monopolies such as electricity networks to keep prices fair.
When comparing structures, focus on barriers to entry and market power, then trace through the effects on price, output, efficiency and long-run profit.