Inside This Unit: The Full Breakdown
This unit examines market structures where firms have some degree of market power: monopoly, monopolistic competition, and oligopoly. Students learn how pricing, output, and efficiency differ from perfect competition when firms can influence price.
Why it matters
Imperfect competition is heavily tested on the AP Micro exam. You must be able to draw diagrams for each market structure, identify profit or loss, and explain the efficiency implications compared to perfect competition.
Key concepts
- A monopoly is a single seller facing the entire market demand curve, with significant barriers to entry preventing competition.
- Monopolists maximize profit at MR = MC but charge the price on the demand curve, which exceeds MR — creating deadweight loss.
- Monopolistic competition features many firms selling differentiated products, with free entry driving long-run economic profit to zero.
- Oligopoly involves a few large firms whose decisions are interdependent, analyzed using game theory and the prisoner's dilemma.
Monopoly
A monopoly exists when a single firm supplies the entire market, protected by barriers to entry such as patents, resource control, economies of scale, or government licensing. The monopolist faces a downward-sloping demand curve, meaning it must lower price to sell additional units. This makes marginal revenue less than price because the price reduction applies to all units sold. The monopolist maximizes profit at MR = MC, then charges the demand curve price for that quantity. The resulting output is lower and price is higher than the competitive outcome, creating deadweight loss. On the AP exam, you must be able to draw and label the monopoly diagram and identify consumer surplus, producer surplus, and deadweight loss.
Monopolistic Competition
Monopolistic competition combines elements of monopoly (product differentiation, downward-sloping demand) with elements of competition (many firms, free entry and exit). In the short run, firms may earn economic profit or suffer losses, depending on the position of their demand curve relative to their cost curves. In the long run, entry and exit drive economic profit to zero — but unlike perfect competition, price exceeds marginal cost, creating a small deadweight loss, and firms operate with excess capacity (producing below the minimum of ATC). This tradeoff between variety and efficiency is a common AP exam topic.
Oligopoly and Game Theory
Oligopolies consist of a few large firms whose decisions are strategically interdependent — each firm must consider how rivals will respond to its pricing and output choices. Game theory, particularly the prisoner's dilemma, models this interdependence. Each firm would earn higher profit if all cooperated (by keeping prices high), but each also has an incentive to cheat by lowering price to capture more market share. This tension between cooperation and competition explains why cartels (agreements to fix prices) tend to be unstable. On the AP exam, you must be able to analyze payoff matrices and identify dominant strategies and Nash equilibria.
AP exam tip
When comparing market structures, always identify three things: the profit-maximizing output (MR = MC), the price charged (from the demand curve), and the efficiency outcome (is there deadweight loss?). This systematic approach works for every market structure question.
Connections to other units
- Unit 2: Perfect competition is the efficiency benchmark against which all imperfectly competitive markets are evaluated.
- Unit 4: Firms with market power in product markets may also have monopsony power in factor markets.
- Unit 5: Government regulation of monopoly and antitrust policy are responses to the inefficiencies identified in this unit.
