Oligopoly & Game Theory: How to Evaluate Collusion in Exams

Oligopoly is one of the most frequently tested market structures in A-Level and IB Economics. Unlike perfect competition or monopoly, firms in an oligopoly are defined by a single crucial characteristic: interdependence.

This means that a firm cannot make decisions about price, output, or advertising without considering the likely reactions of its rivals. To evaluate oligopolies in exams, you must be comfortable using two key analytical tools: the Kinked Demand Curve and Game Theory.

Understanding Oligopoly and Interdependence

An oligopoly is a market structure dominated by a few large firms. The high concentration ratio means that the actions of one firm directly impact the others.

Key characteristics include:

* High barriers to entry and exit. * Differentiated products (though sometimes homogeneous). * Non-price competition (such as branding and advertising). * Mutual interdependence among firms.

Because of this interdependence, firms face a constant dilemma: should they compete aggressively to win market share, or collude with rivals to maximize joint profits?

The Kinked Demand Curve and Price Rigidity

The Kinked Demand Curve model illustrates why prices in an oligopoly often remain stable, even if costs change. It is based on two behavioral assumptions about how rivals react to a firm's pricing decisions.

If a firm raises its price, rivals will not follow. They will keep their prices low to steal market share. Therefore, demand is highly price elastic above the current price.

If a firm lowers its price, rivals will follow suit to protect their market share. Therefore, demand is price inelastic below the current price.

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This creates a "kink" in the Average Revenue (AR) curve and a discontinuous Marginal Revenue (MR) curve.

Key takeaways for your exam:

* The vertical gap in the MR curve means Marginal Cost (MC) can fluctuate within this range without changing the profit-maximizing price or quantity. * This explains price stickiness or price rigidity in non-collusive oligopolies. * Firms prefer to compete on quality, customer service, or advertising rather than price.

Game Theory and The Prisoner's Dilemma

While the Kinked Demand Curve explains price stability, Game Theory explains the strategic decision-making process. The most common model used in exams is the Prisoner's Dilemma.

Imagine two firms, Firm A and Firm B, deciding whether to set a High Price or a Low Price.

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Let's break down the strategic choices:

* If both firms collude and set a High Price, they maximize joint profits. * However, there is a strong incentive to cheat. If Firm A sets a Low Price while Firm B sets a High Price, Firm A captures the market and makes a massive profit. * Because both firms fear being undercut, they both choose the Low Price.

This results in a Nash Equilibrium where both firms end up worse off than if they had colluded. The Low Price strategy is often the dominant strategy—the best choice for a firm regardless of what the other firm does.

Collusion: Overt vs. Tacit

To escape the Prisoner's Dilemma, firms may attempt to collude.

There are two main types of collusion:

* Overt Collusion: A formal, explicit agreement to fix prices or share markets (e.g., a cartel like OPEC). This is illegal in most countries. * Tacit Collusion: An unspoken, informal understanding to avoid price wars, often led by a dominant firm (price leadership).

For collusion to be successful and sustainable, several conditions must be met:

* A small number of firms in the industry. * Similar costs of production among firms. * High barriers to entry to prevent new firms from undercutting the cartel. * Ineffective government regulation or anti-trust enforcement.

How to Evaluate Oligopoly in Exams

To score top marks in your essays, you must evaluate these models critically. Here are some key evaluation points:

* Limitations of the Kinked Demand Curve: The model explains why prices are sticky, but it fails to explain how the original price was set in the first place. * Real-world complexities: Game theory matrices in exams usually assume perfect information and only two choices. In reality, firms make dynamic decisions over time, allowing for strategies like "tit-for-tat," which can sustain tacit collusion. * The role of contestability: Even if an oligopoly is highly concentrated, the threat of new entrants (if sunk costs are low) might force firms to behave competitively rather than colluding. * Dynamic efficiency: Oligopolies often earn supernormal profits in the long run. Evaluate whether they reinvest these profits into Research & Development (R&D), leading to dynamic efficiency and consumer benefits.

Mastering these models will give you a solid framework for tackling any oligopoly question. Remember to draw accurate diagrams and apply the specific industry context provided in your exam case study!