10.2 Oligopoly

Oligopoly

Oligopoly describes a market structure where a small number of large firms dominate an industry. Because so few firms control the market, each one has real power to influence prices, and every decision one firm makes ripples through to the others. Understanding oligopoly means understanding strategic interdependence: firms can't just optimize in isolation the way a monopolist or a perfectly competitive firm can.

Small Number of Large Firms

What sets oligopoly apart from other market structures is interdependence. Each firm's pricing, output, and strategy decisions directly affect the profits of its rivals, so every move requires thinking about how competitors will respond.

A few defining features:

• Few dominant firms, each with significant market power to influence prices
• High barriers to entry keep new competitors out. These barriers include economies of scale, large startup costs, patents, and control of key resources.
• Products can be homogeneous or differentiated. Homogeneous oligopolies sell nearly identical goods (steel, aluminum, crude oil). Differentiated oligopolies sell products with distinct branding or features (smartphones, automobiles, airlines).

Because firms are interdependent, an oligopolist can't simply set its price by looking at its own cost curves. It has to anticipate how rivals will react. If Ford cuts prices on trucks, GM and Ram have to decide whether to match, undercut, or hold steady. This back-and-forth is what makes oligopoly analysis so different from the other market structures you've studied.

Competition vs. Collusion

Oligopolists face a fundamental tension: compete independently, or cooperate to maximize joint profits?

• Competition can trigger price wars, driving prices down toward marginal cost and shrinking profits for everyone.
• Collusion means firms coordinate on prices or output levels to act more like a shared monopoly, earning higher profits together.

Collusion takes two forms:

• Explicit collusion (cartels): Firms formally agree to fix prices or limit output. OPEC is the most well-known example. In most countries, cartels are illegal under antitrust law.
• Tacit collusion: Firms reach informal understandings without direct communication. For instance, one firm acts as a "price leader," and others follow its pricing without any written agreement.

The core problem with collusion is that cartels are inherently unstable. Every member has an incentive to cheat by secretly lowering its price or producing more than its quota. If one firm cheats, it captures a larger share of the market at the expense of the others. This is exactly why game theory is so useful for analyzing oligopoly behavior.

Prisoner's Dilemma

The prisoner's dilemma is a game theory model that captures the tension between cooperation and self-interest. Here's the classic setup:

1. Two suspects are arrested and interrogated in separate rooms.
2. Each must independently choose to confess or remain silent.
3. The outcomes depend on what both choose:
   • Both remain silent: each gets a light sentence (1 year)
   • Both confess: each gets a moderate sentence (5 years)
   • One confesses, the other stays silent: the confessor goes free, the silent suspect gets a heavy sentence (10 years)

Even though both suspects would be better off staying silent (1 year each), the dominant strategy for each is to confess. No matter what the other person does, confessing gives you a better individual outcome. When both follow this logic, they land on the worst combined result (5 years each). This outcome where neither player can improve by changing strategy alone is called a Nash equilibrium.

Applying this to oligopoly: Replace "confess" with "compete aggressively" and "remain silent" with "collude."

• If both firms collude (keep prices high), they share monopoly-level profits.
• If both compete (cut prices), profits fall for everyone.
• If one firm undercuts while the other holds prices high, the undercutter grabs market share and earns even more.

The Nash equilibrium is for both firms to compete, even though mutual collusion would make them both better off. This is exactly why cartels tend to break down. Each member faces a constant temptation to cheat for short-term gain, which undermines the long-term cooperative outcome.