How do firms behave when there are many differentiated rivals, or only a few interdependent ones?
Compare monopolistic competition and oligopoly, explaining product differentiation, interdependence, collusion and non-price competition
A focused answer to the H2 Economics learning outcome on monopolistic competition and oligopoly. Differentiation and long-run normal profit in monopolistic competition, and interdependence, collusion, price rigidity and non-price competition in oligopoly.
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What this dot point is asking
SEAB wants you to compare monopolistic competition and oligopoly, explaining product differentiation, interdependence, collusion and non-price competition. The central insight is that most real markets lie between the extremes of perfect competition and monopoly, and these two structures capture the two most common middle cases: many differentiated firms, and a few interdependent ones.
The answer
Monopolistic competition
Monopolistic competition combines features of both extremes:
- Many firms, each small relative to the market.
- Differentiated products (by brand, quality, location or service), so each firm faces a downward-sloping but elastic demand curve and has slight price-setting power.
- Easy entry and exit, with low barriers.
Short run. The firm maximises profit where and can earn supernormal profit if .
Long run. Easy entry means rivals enter to share any supernormal profit, taking demand away. Each firm's demand curve shifts left until it is tangent to the AC curve, where and only normal profit is earned. Because the demand curve slopes down, this tangency lies to the left of minimum AC, so the firm operates with excess capacity and is not productively efficient. It is also allocatively inefficient (), though only mildly, given fairly elastic demand.
Oligopoly
Oligopoly is a market dominated by a few large firms, with high barriers to entry and a high concentration ratio. Its defining feature is interdependence:
Price rigidity and the kinked demand curve
A simple model of interdependence is the kinked demand curve. A firm assumes that if it cuts price, rivals will match it (so it gains little, demand is inelastic below the current price), but if it raises price, rivals will not follow (so it loses a lot of market share, demand is elastic above the current price). The demand curve is kinked at the current price, producing a vertical gap in marginal revenue, so price tends to be rigid even when costs change.
Collusion and non-price competition
To escape the risk of mutually destructive price wars, oligopolists may:
- Collude. Form a cartel (often illegal) or tacitly coordinate to act like a monopoly, raising price and profit. Collusion is unstable because each firm has an incentive to cheat by undercutting.
- Compete on non-price terms. Advertising, branding, product quality, loyalty schemes and innovation build market share without triggering a price war.
Game theory (such as the prisoner's dilemma) formalises why collusion is tempting but fragile: each firm's best individual move can undermine a deal that would benefit them all.
Examples in context
Example 1. Singapore's food and retail scene. The restaurant and cafe market is close to monopolistic competition: many outlets sell differentiated meals, each with a little pricing power from location and brand, but easy entry keeps long-run profits near normal and capacity tends to exceed the efficient level, with frequent openings and closures.
Example 2. Telecoms and supermarkets as oligopolies. Mobile telecoms and grocery retail are dominated by a few large players. Prices on headline plans or staple goods tend to move together and rarely undercut sharply, while the firms compete fiercely on data allowances, store experience, loyalty programmes and advertising, the classic oligopoly mix of price rigidity and intense non-price competition.
Try this
Q1. State two features of monopolistic competition. [2 marks]
- Cue. Many firms selling differentiated products, and easy entry and exit (so long-run profit is normal).
Q2. Explain why prices may be rigid in an oligopoly. [3 marks]
- Cue. Each firm assumes rivals will match a price cut (so it gains little) but not a price rise (so it loses share); the kinked demand curve this implies makes price changes unattractive in either direction.
Q3. Why is a cartel unstable? [2 marks]
- Cue. Each member can earn more by secretly undercutting the agreed price to win sales, so every firm has an incentive to cheat, which tends to break the collusion down.
Exam-style practice questions
Practice questions written in the style of SEAB exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Original10 marksExplain why a monopolistically competitive firm earns supernormal profit in the short run but only normal profit in the long run.Show worked answer →
A 10 mark question rewards the differentiated-but-easy-entry setup, the short-run profit, and the long-run entry result.
- Setup
- Many firms sell differentiated (slightly different) products, so each faces a downward-sloping but fairly elastic demand curve and has some price-setting power. Entry is easy.
- Short run
- The firm maximises profit where . If price exceeds average cost at that output, it earns supernormal profit.
- Long run
- Easy entry means new firms enter to share the supernormal profit, taking demand away from existing firms. Each firm's demand curve shifts left until it is tangent to the average cost curve. Now at the profit-maximising output, so only normal profit is earned and entry stops.
- Note
- Because the demand curve is downward-sloping, the tangency is to the left of minimum AC, so the firm is not productively efficient (it has excess capacity).
Markers reward the differentiation and easy entry, the short-run supernormal profit, the entry-driven leftward shift to tangency, and ideally the excess-capacity point.
Original9 marksExplain why firms in an oligopoly are interdependent, and discuss why they may compete on non-price terms rather than price.Show worked answer →
A 9 mark question rewards interdependence, the incentive to avoid price wars, and the forms of non-price competition.
- Interdependence
- A few large firms dominate, so each firm's actions noticeably affect rivals, who react. Each must therefore anticipate rivals' responses when setting price or output.
- Why avoid price competition
- A price cut may be matched by rivals, triggering a price war that lowers everyone's profit, while a price rise may not be followed, losing market share. This creates an incentive for price stability (illustrated by the kinked demand curve, where rivals match cuts but not rises, making demand kinked and price rigid).
- Non-price competition
- To compete without risking a price war, firms use advertising, branding, product quality, loyalty schemes and innovation. These build market share and brand loyalty while keeping prices stable.
Markers reward the interdependence definition, the price-war and asymmetric-response reasoning for price rigidity, and at least two forms of non-price competition.
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