Oligopoly

When a Few Firms Run the Show

You might assume that having three or four competitors in a market produces something close to competition. Prices should be driven down, consumers should benefit, firms should fight tooth and nail for every sale. That assumption is wrong — and the U.S. wireless industry proves it. Verizon, AT&T, and T-Mobile all charge roughly the same for unlimited plans, hovering within a few dollars of each other month after month. When Delta raises fares on the Atlanta-to-Chicago route, United matches within hours. The textbook explanation is one word: mutual interdependence.

An oligopoly is a market dominated by a small number of large firms. Cell carriers. Airlines. Auto manufacturers. Streaming services. Unlike perfect competition (where your firm is too small to move the needle) or monopoly (where you are the market), oligopoly sits in the messy, strategic middle ground. You have real market power, but so do your rivals. Every pricing decision, every ad campaign, every product launch sends ripples through the entire industry.

That interdependence is what separates oligopoly from everything else. A monopolist worries about consumer demand and nothing more. A perfectly competitive firm takes the market price and moves on. An oligopolist plays chess. If Coca-Cola slashes prices by 15%, Pepsi must decide: match the cut, undercut further, or hold firm and hope brand loyalty carries the day? Each response triggers another round of decisions.

Barriers to entry keep the club small. Building a 5G network costs tens of billions of dollars. Pharmaceutical patents last 20 years. Brand loyalty built over decades — think Nike, Apple, Boeing — is nearly impossible for a startup to replicate overnight. New firms want in because oligopoly profits can be enormous, but the barriers make entry brutally difficult.

Products can be identical (steel, aluminum — a homogeneous oligopoly) or differentiated (Samsung Galaxy vs. iPhone). Strategic interdependence remains either way.

Game Theory and the Prisoner's Dilemma

Picture yourself as a pricing executive at American Airlines. You could slash fares on the Chicago-to-Miami route by 20% and steal passengers from United. Sounds like a win — until United retaliates with a 25% cut, Southwest jumps in, and everyone's margins are destroyed. Both airlines would have earned more by keeping prices high.

This is why economists use game theory: the study of strategic decision-making when your outcome depends on what the other player does. In oligopoly, firms don't just react to supply and demand curves. They anticipate each other's moves, bluffs, and retaliations.

The classic illustration is the prisoner's dilemma. Applied to airline pricing:

Setup: American and United each choose between keeping fares high or cutting low.
- Both keep fares high → each earns $10 million
- Both cut fares → price war, each earns $4 million
- One cuts while the other holds high → the cutter grabs market share and earns $12 million; the holdout earns just $2 million

Each airline individually gains by cutting fares regardless of what the other does. If United holds high, American earns $12M by cutting versus $10M by holding. If United cuts, American earns $4M by cutting versus $2M by holding. Cutting is the dominant strategy for both players. Yet when both cut, they land at $4M each — far worse than the $10M they'd each pocket through cooperation.

The tension between individual rationality and collective interest is the beating heart of oligopoly. Firms desperately want to cooperate and keep prices high, but the temptation to cheat is overwhelming.

Nash Equilibrium and Dominant Strategies

Where do the airlines actually end up? The answer comes from John Nash, the Princeton mathematician made famous by the 2001 film A Beautiful Mind.

A Nash equilibrium occurs when no player can improve their payoff by unilaterally switching strategy, given what the other player is doing. In the airline example, both cutting fares is the Nash equilibrium. Once both are cutting, neither benefits from switching alone to high fares — they'd just hemorrhage market share.

The painful part: the Nash equilibrium is not the best collective outcome. Both firms stuck at $4M is strictly worse than both earning $10M. But it's stable. Neither has incentive to deviate on its own.

A dominant strategy exists when one choice beats the alternative no matter what the opponent does. In the prisoner's dilemma, cutting fares is dominant for both airlines. Not every game has dominant strategies, though. In more complex scenarios with three or four options, the best move genuinely depends on your read of the competition, and no single choice dominates across all possibilities.

For the AP exam: Nash equilibrium is where rational, self-interested firms end up, not where they'd like to be. That gap between the Nash outcome and the cooperative outcome is precisely what tempts firms toward collusion.

Cartels and Collusion

If cutting prices makes everyone worse off, the obvious question is: why not just agree to keep them high? That logic drives collusion — rival firms secretly or openly coordinating on pricing, output, or market territory to maximize joint profits.

OPEC (Organization of the Petroleum Exporting Countries) is the most famous example. Saudi Arabia, Iraq, the UAE, and other member nations meet regularly to set production quotas. Restricting oil output pushes the global price above the competitive level. When OPEC coordination is tight — as it was in the 1973 embargo that quadrupled oil prices — members split enormous profits. When discipline collapses, prices crater.

A cartel is collusion made formal: firms explicitly agree on prices or output. When it works, a cartel mimics a monopoly outcome — restricted quantity, monopoly-level prices, deadweight loss. That's why cartels are illegal in most countries. The Sherman Antitrust Act of 1890 made price-fixing a federal crime in the United States.

Every cartel faces the same fatal flaw, though. Cheating is irresistible. If American and United agree to keep fares high and each earns $10M, American knows it could secretly discount flights, grab extra passengers, and jump to $12M while United naively holds the line. Every cartel member faces this exact temptation. Cartels are therefore inherently unstable.

OPEC demonstrates the instability constantly. Member countries routinely exceed their production quotas, pumping extra oil for additional revenue and hoping nobody notices. When enough members cheat, discipline collapses and prices fall.

Collusion is easier to maintain when:
- Fewer firms are involved, making monitoring simpler
- The product is homogeneous, so secret discounting is hard to hide
- Demand conditions are stable rather than volatile
- Firms interact repeatedly over time, because the threat of future punishment keeps everyone honest (the so-called "grim trigger" strategy in repeated games)

Even without explicit agreements, firms sometimes engage in tacit collusion — coordinating behavior without direct communication. One airline raises fares and others follow within hours. Proving a secret agreement is nearly impossible, so it's technically legal, but the economic effects mirror those of an outright cartel.

The Kinked Demand Curve

Oligopoly prices are often remarkably sticky. Gas stations on the same intersection hold identical prices for weeks. Airlines lock fares on popular routes. The kinked demand curve model offers an explanation rooted in one simple assumption about how rivals react.

If you raise your price, competitors won't follow. They happily watch your customers defect to them. Demand above the current price is therefore very elastic — a small price increase triggers a large drop in your sales.

If you cut your price, competitors match immediately. They refuse to lose market share. Demand below the current price is relatively inelastic, because a price cut barely boosts your sales when rivals neutralize it.

This asymmetry creates a kink in the demand curve at the current price. The kink produces a vertical gap in the marginal revenue curve. Even if a firm's MC shifts up or down within that gap, the profit-maximizing quantity — and therefore the price — doesn't change.

So prices are sticky because firms resist raising them (you lose customers) and resist cutting them (rivals match, leaving everyone with thinner margins and roughly the same market share). Prices cluster together and stay put until costs or demand shift dramatically enough to push MC outside the gap.

The model has real limitations. It explains why prices are rigid but not how the initial price got set. Economists like George Stigler criticized it back in the 1940s for exactly that reason. Still, it captures something genuine about oligopoly behavior, and it appears on the AP exam regularly enough that you need to know it.

Worked Example: 2-Firm Payoff Matrix

Samsung and Apple are deciding whether to spend big on advertising or keep ad budgets low.

Payoff matrix (profits in millions, Samsung listed first):

Apple: High Ads Apple: Low Ads
Samsung: High Ads (5, 5) (9, 2)
Samsung: Low Ads (2, 9) (7, 7)

Samsung's dominant strategy:
- If Apple chooses High Ads: Samsung earns $5M (High) vs. $2M (Low). High Ads wins.
- If Apple chooses Low Ads: Samsung earns $9M (High) vs. $7M (Low). High Ads wins again.
- Samsung's dominant strategy: High Ads regardless of Apple's choice.

Apple's dominant strategy:
- If Samsung chooses High Ads: Apple earns $5M (High) vs. $2M (Low). High Ads wins.
- If Samsung chooses Low Ads: Apple earns $9M (High) vs. $7M (Low). High Ads wins again.
- Apple's dominant strategy: High Ads.

Nash equilibrium: Both firms choose High Ads, earning ($5M, $5M). Neither can improve by switching alone. If Samsung moves to Low Ads while Apple stays at High Ads, Samsung drops from $5M to $2M. Same logic for Apple.

Cooperative outcome: If both committed to Low Ads, they'd each earn $7M — $2M more per firm. But the agreement is unstable. If Apple trusts Samsung to keep ads low, Samsung can defect to High Ads and jump from $7M to $9M. The incentive to cheat destroys cooperation, which is the prisoner's dilemma in action. Rational self-interest pushes both firms to the Nash equilibrium ($5M each), even though mutual restraint ($7M each) would be collectively superior.