Theme 3: Business Behaviour and the Labour Market — 3.4.4 Oligopoly
Welcome to your study guide on Oligopoly! If you have ever wondered why smartphone prices rarely change drastically overnight, or why major supermarkets are constantly matching each other's prices and launching loyalty point schemes, you are already observing an oligopoly in action. This chapter is central to Edexcel Economics A (Paper 1 and Paper 3). Don't worry if concepts like game theory or kinked demand curves seem intimidating at first — we will break them down step-by-step.
1. What is an Oligopoly?
An oligopoly is a market structure dominated by a small number of large firms. While there may be many smaller businesses operating on the fringes, the market power is concentrated in the hands of the top few.
Core Characteristics
To identify an oligopoly in your exam, look for these key features:
• A Few Large Dominant Firms: A handful of firms supply the vast majority of output in the industry.
• High Barriers to Entry and Exit: It is very difficult for new competitors to enter the industry. Barriers include high start-up costs (sunk costs), strong brand loyalty, patents, and large economies of scale enjoyed by incumbent firms.
• High Concentration Ratio: A high proportion of total market sales is held by the top firms.
• Interdependence: This is the single most important defining trait! Interdependence means that the actions of one firm (such as changing price, launching an advertising blitz, or updating a product) directly impact rivals and trigger a reaction from them. A firm cannot make decisions in isolation.
• Product Differentiation: Products are rarely identical. Firms use branding, packaging, design, and advertising to distinguish their goods from competitors (e.g., Apple iOS vs. Samsung Android).
Quick Memory Aid: Remember the acronym B-I-N-D:
B — Barriers to entry are high
I — Interdependence between firms
N — Non-price competition is heavily used
D — Differentiated products
Key Takeaway: An oligopoly is dominated by a few large firms whose decisions directly depend on and affect each other due to high market concentration and strong barriers to entry.
2. Measuring Market Power: Concentration Ratios
How do economists officially decide whether a market is an oligopoly? They calculate a concentration ratio.
Calculating the \(n\)-Firm Concentration Ratio
The \(n\)-firm concentration ratio measures the total market share held by the largest \(n\) firms in the industry. It is calculated by adding up their individual percentage market shares:
\(\text{Concentration Ratio } (CR_n) = \sum \text{Market shares of the top } n \text{ firms}\)
Worked Example:
Imagine a market with the following shares for the top 5 firms:
• Firm A: \(24\%\)
• Firm B: \(18\%\)
• Firm C: \(14\%\)
• Firm D: \(10\%\)
• Firm E: \(6\%\)
To find the 3-Firm Concentration Ratio (\(3CR\)):
\(3CR = 24\% + 18\% + 14\% = 56\%\)
To find the 5-Firm Concentration Ratio (\(5CR\)):
\(5CR = 24\% + 18\% + 14\% + 10\% + 6\% = 72\%\)
The Oligopoly Benchmark Threshold
Under the Edexcel syllabus, a common benchmark for an oligopoly is a 5-firm concentration ratio (\(5CR\)) of \(60\%\) or higher. When the top 5 firms control \(60\%\) or more of total sales, the market exhibits strong oligopolistic characteristics and high interdependence.
Key Takeaway: Concentration ratios show how concentrated market power is. If the \(5CR \ge 60\%\), the market is classified as an oligopoly.
3. Collusive vs. Non-Collusive Behaviour
Because firms in an oligopoly are interdependent, they face a strategic choice: do they fight each other for market share, or do they cooperate to maximise joint profits?
A. Collusive Behaviour
Collusion occurs when firms agree to limit competition, coordinate prices, or restrict output to increase collective profits.
• Overt Collusion: A formal, explicit, and open agreement between firms. A formal collusive agreement is known as a Cartel. Firms openly meet to fix prices or divide territories. Note: Overt collusion is illegal in the UK, EU, and US because it harms consumers through artificially high prices.
• Tacit Collusion: An informal, unwritten understanding between firms to avoid price competition without any direct communication. The most common form is Price Leadership. This happens when the largest or most dominant firm sets the market price, and smaller rival firms quietly follow that price lead to avoid a damaging price war.
B. Non-Collusive Behaviour
Non-collusive behaviour occurs when firms act independently and competitively. Even though they do not communicate or cooperate, each firm carefully anticipates how rivals will react before making any pricing or marketing moves.
Key Takeaway: Collusion is an agreement to restrict competition (either through illegal formal cartels or tacit price leadership), while non-collusive firms act independently while remaining aware of rival reactions.
4. Game Theory and the Payoff Matrix
To understand non-collusive decision-making, economists use Game Theory. Game theory models strategic interactions between firms where the outcome for each depends on the choices of both.
The Prisoner's Dilemma
The Prisoner's Dilemma illustrates why two rational firms might fail to cooperate, even when cooperation would produce the best joint outcome.
Interpreting a \(2 \times 2\) Payoff Matrix
Let's examine two rival supermarket chains, Firm X and Firm Y, deciding whether to set a High Price or a Low Price. The numbers in each box represent profit in millions of pounds (\(\text{Profit for Firm X}, \text{Profit for Firm Y}\)):
Outcome Matrix:
• Both set High Price: (\(£50\text{m}, £50\text{m}\)) — Collusive outcome / Joint profit maximisation
• Firm X sets Low Price, Firm Y sets High Price: (\(£70\text{m}, £10\text{m}\)) — Firm X undercuts and steals market share
• Firm X sets High Price, Firm Y sets Low Price: (\(£10\text{m}, £70\text{m}\)) — Firm Y undercuts and steals market share
• Both set Low Price: (\(£30\text{m}, £30\text{m}\)) — Nash Equilibrium
Step-by-Step Analysis: Finding the Dominant Strategy
A dominant strategy is the best choice for a firm regardless of what its rival decides to do.
1. Look at Firm X's perspective:
• If Firm Y chooses High Price: Firm X gets \(£50\text{m}\) by picking High, or \(£70\text{m}\) by picking Low. Firm X picks Low.
• If Firm Y chooses Low Price: Firm X gets \(£10\text{m}\) by picking High, or \(£30\text{m}\) by picking Low. Firm X picks Low.
Conclusion: Firm X's dominant strategy is always to set a Low Price.
2. Look at Firm Y's perspective:
• If Firm X chooses High Price: Firm Y gets \(£50\text{m}\) by picking High, or \(£70\text{m}\) by picking Low. Firm Y picks Low.
• If Firm X chooses Low Price: Firm Y gets \(£10\text{m}\) by picking High, or \(£30\text{m}\) by picking Low. Firm Y picks Low.
Conclusion: Firm Y's dominant strategy is always to set a Low Price.
Nash Equilibrium
A Nash Equilibrium is reached when neither firm can improve its payoff by unilaterally changing its strategy, given the strategy chosen by the competitor. In this matrix, the Nash Equilibrium is (Low Price, Low Price) earning \(£30\text{m}\) each. Even though both would be better off at \((£50\text{m}, £50\text{m})\), the fear of being undercut and the incentive to cheat leads them to the lower profit outcome.
Key Takeaway: Due to self-interest and lack of trust, non-collusive firms often end up at a Nash Equilibrium with lower profits than if they successfully colluded.
5. Pricing Strategies and Non-Price Competition
Because price competition can quickly lead to mutually destructive outcomes, oligopolists deploy specific pricing tactics and rely heavily on non-price competition.
Pricing Strategies
• Price Wars: When non-collusive firms aggressively and repeatedly undercut one another's prices to capture market share. While great for consumers in the short term, price wars severely compress profit margins.
• Predatory Pricing: An aggressive strategy where an established firm deliberately sets its price below Average Variable Cost (\(P < AVC\)) in the short run to force an existing competitor out of the market. Once the rival exits, the predator raises prices back up. Note: This practice is illegal under competition law.
• Limit Pricing: Setting prices low enough to deter potential new entrants from entering the market in the first place. The incumbent firm sets the price just below the average cost of potential competitors, sacrificing some short-term profit to maintain long-term monopoly power.
Non-Price Competition
To avoid price wars, oligopolists compete through non-price methods, including:
• Advertising and Branding: Building brand loyalty so consumers remain loyal even if rival prices change.
• Quality and Customer Service: Improving product reliability, speed of delivery, or after-sales support.
• Loyalty Schemes: Programmes such as supermarket loyalty cards (e.g., Clubcards) and reward points that lock customers into repeat purchases.
Key Takeaway: Oligopolists prefer non-price competition because price wars erode profits. When price tactics are used, they distinguish between illegal predatory pricing (aimed at existing rivals) and limit pricing (aimed at future entrants).
6. The Kinked Demand Curve and Price Rigidity
Why do prices in oligopoly markets remain stable for long periods, even when business costs change? Economists explain this price rigidity using the Kinked Demand Curve model.
The Model's Core Assumptions
The kinked demand curve assumes an asymmetrical reaction from rivals:
1. If a firm increases its price above the current market price (\(P_1\)): Rivals will not follow. Consumers will switch to the cheaper competitors, meaning demand is highly price elastic (\(PED > 1\)). The firm suffers a large loss in quantity sold and total revenue falls.
2. If a firm decreases its price below the current market price (\(P_1\)): Rivals will immediately match the price cut to avoid losing their customers. The price-cutting firm gains very few extra sales, meaning demand is price inelastic (\(PED < 1\)). Total revenue falls.
Visualising the Diagram
• Axes: The vertical axis must be labelled Price and Costs, and the horizontal axis must be labelled Quantity.
• Demand Curve (\(AR\)): Shows a visible "kink" precisely at the prevailing market price \(P_1\) and quantity \(Q_1\). The segment above \(P_1\) is relatively flat (elastic), and the segment below \(P_1\) is steep (inelastic).
• Marginal Revenue Curve (\(MR\)): Because the slope of the \(AR\) curve changes abruptly at \(Q_1\), the \(MR\) curve splits, creating a vertical gap (discontinuity) directly beneath the kink.
• Cost Changes: The Marginal Cost (\(MC\)) curve passes through this vertical gap. If marginal costs rise or fall within this gap (from \(MC_1\) to \(MC_2\)), the profit-maximising output remains unchanged at \(Q_1\) and the price stays rigid at \(P_1\).
Key Takeaway: The kinked demand curve demonstrates why prices are "sticky" or rigid in oligopoly: raising prices loses customers, cutting prices starts a price war, and cost shifts within the \(MR\) gap do not alter the profit-maximising price.
7. Common Exam Pitfalls and How to Avoid Them
Examiners frequently highlight recurring errors in student responses on Oligopoly. Keep these top tips in mind:
• Pitfall 1: Confusing Predatory Pricing and Limit Pricing
Correction: Predatory pricing aims to destroy an existing rival by pricing below \(AVC\). Limit pricing is designed to deter potential future entrants from entering the market.
• Pitfall 2: Incorrect Kinked Demand Curve Diagrams
Correction: Always label the vertical axis Price / Costs and horizontal axis Quantity. Ensure the "kink" on the \(AR\) curve aligns directly with the vertical gap in the \(MR\) curve at \(P_1\) and \(Q_1\).
• Pitfall 3: Incomplete Game Theory Explanations
Correction: Do not just state the final Nash Equilibrium quadrant. You must explicitly talk through each firm's dominant strategy step-by-step: "If Firm A does X, Firm B gets... whereas if Firm A does Y, Firm B gets..."
• Pitfall 4: Quoting Data Without Economic Analysis
Correction: If a data-response question gives market share numbers, do not just repeat them. Calculate the \(CR_3\) or \(CR_5\) and explain that high concentration creates strong interdependence.
Quick Summary Checklist
Before sitting your exam, make sure you can confidentially:
✓ State the 5 core characteristics of an oligopoly (B-I-N-D).
✓ Calculate an \(n\)-firm concentration ratio and recall the \(5CR \ge 60\%\) threshold.
✓ Distinguish between overt collusion (cartels) and tacit collusion (price leadership).
✓ Solve a \(2 \times 2\) Game Theory payoff matrix to identify dominant strategies and the Nash Equilibrium.
✓ Differentiate predatory pricing from limit pricing and give examples of non-price competition.
✓ Draw and explain the Kinked Demand Curve and why it leads to price rigidity.