Oligopoly: Price, Output, and Pricing Strategy

Updated for the 2026-2027 CFA® Level I curriculum.

An oligopoly is a market with a few dominant firms that watch each other closely. Every pricing decision one firm makes can trigger a reaction from rivals, so there is no single demand curve or pricing rule that applies to all oligopoly questions. This reading tests whether you can match the right model, kinked demand, Cournot, Nash equilibrium, collusion, or price leadership, to the situation described, then apply MR = MC correctly within that model.

Key Takeaways

• Oligopoly means a few firms hold significant market share and each firm's decisions affect the others directly.

• The kinked demand model assumes rivals match price cuts but ignore price increases, which creates price rigidity.

• Cournot competition has each firm choosing output while assuming rival output stays fixed, producing a stable equilibrium between monopoly and perfect competition outcomes.

• A Nash equilibrium is the outcome where no firm gains by changing its strategy alone, and it is often not the outcome with the highest combined profit.

• Collusion raises joint profit but is hard to sustain because each firm has an incentive to cheat on the agreement.

• A dominant firm sets output where its MR equals MC using its residual demand, and smaller firms follow its price.

• Oligopoly has no well-defined supply curve because output depends on strategic assumptions, not just price and marginal cost.

What You Need to Know for CFA Level I

• Recognize oligopoly from a few dominant firms, high entry barriers, and strategic interdependence.

• Explain the assumption and implication of the kinked demand model.

• Explain Cournot quantity competition and why each firm treats rival output as fixed.

• Identify a Nash equilibrium from a payoff matrix.

• Explain why collusion can raise joint profit and why agreements are difficult to sustain.

• Explain dominant-firm price leadership and follower behavior.

• State why oligopoly has no well-defined supply curve.

• Apply  only after identifying the relevant demand and strategic setting.

What Is An Oligopoly?

A small number of firms account for most of the output in an oligopoly market. Products can be standardized, like steel or airline seats, or differentiated, like smartphones or soft drinks. Entry barriers are significant, often from economies of scale, capital requirements, or control of key inputs.

The defining feature is interdependence. Each firm's price, output, and marketing decisions affect its rivals, and each firm knows it. A firm cannot set price or output without thinking about how competitors will respond. This is the core distinction from monopolistic competition, where firms largely ignore each other's individual moves.

Why Oligopoly Pricing Is Interdependent

A price cut by one firm often pulls customers away from rivals. Those rivals frequently match the cut to protect market share, which limits the gain from cutting price in the first place.

A price increase behaves differently. Rivals may choose not to follow, hoping to gain customers from the firm that raised price. That firm then risks losing significant volume.

This asymmetry extends beyond price. Advertising campaigns, capacity expansions, and new product launches can also draw a competitive response. Not every oligopoly colludes. Interdependence describes strategic awareness, not automatic cooperation.

Kinked Demand Curve and Price Rigidity

The kinked demand model assumes rivals match price cuts but do not match price increases. This creates two different demand segments around the current price.

Above the prevailing price, demand is relatively elastic. Customers switch to competitors who did not raise their price, so a price increase causes a large drop in quantity sold. Below the prevailing price, demand is relatively inelastic. Rivals match the cut, so the firm gains little volume relative to the price given up.

This kink in the demand curve creates a gap, or discontinuity, in the marginal revenue curve at the current output level. Marginal cost can rise or fall within that gap without changing the profit-maximizing price or output. This explains why oligopoly prices often stay stable even when costs shift moderately.

The model has a real limitation. It explains why price stays fixed once established, but it does not explain how the original prevailing price was set

Cournot Quantity Competition

In the Cournot model, firms compete by choosing output rather than price. Each firm selects its own quantity assuming its rival's quantity stays fixed. Both firms adjust their output based on this assumption until neither wants to change further. That stable point is the Cournot equilibrium.

The intuition matters more than the algebra at Level I. Each firm's reaction function shows its best output choice given any output level chosen by the rival. Where these two reaction functions intersect, both firms are producing their profit-maximizing quantity given the other's choice.

The Cournot outcome sits between the extremes of market structure. Compared with a monopoly, Cournot firms produce more combined output and charge a lower price. Compared with perfect competition, Cournot firms produce less output and charge a higher price. As more firms compete under Cournot assumptions, the outcome moves closer to the competitive result.

Nash Equilibrium and Strategic Decisions

A Nash equilibrium is a set of strategies, one for each firm, where no firm can improve its outcome by changing its own strategy while rivals hold theirs fixed. It applies broadly to strategic settings, including pricing decisions shown in a payoff matrix.

To find a Nash equilibrium, check each firm's best response to every possible choice by the rival. A cell in the payoff matrix is a Nash equilibrium only if both firms are simultaneously playing their best response to the other.

A critical distinction: the Nash equilibrium is not automatically the outcome with the highest combined profit. Firms often reach a Nash equilibrium that leaves both worse off than they would be under coordinated behavior. This gap is exactly why collusion has appeal, even though it is difficult to sustain.

Collusion and Cartels

Collusion occurs when firms coordinate price or output to maximize their joint profit rather than compete independently.

A successful cartel behaves like a single monopolist, restricting total output and raising price above the level that would result from independent decisions.

Certain conditions make collusion easier to sustain: few firms, similar products, similar cost structures, frequent small orders that make cheating easy to detect, credible threats of retaliation against cheaters, and limited competition from outside the cartel.

Even under favorable conditions, collusion faces a structural problem. Each member has an incentive to cheat by secretly undercutting the agreed price to capture extra sales. If enough members cheat, the cartel breaks down. New entrants attracted by high cartel profits can also erode the arrangement over time. Explicit price-fixing agreements are generally restricted by competition law in most jurisdictions, though the details vary and are outside the scope of this note.

Dominant-Firm Price Leadership

In some oligopolies, one large, often lower-cost firm sets the price and smaller firms follow. The leader estimates the residual demand it faces after accounting for the output that smaller firms will supply at any given price. The leader then chooses output where its MR equals its MC and sets price from that residual demand curve.

Follower firms treat the leader's price as given and supply their share of remaining market demand at that price. Followers generally accept this arrangement because undercutting a lower-cost leader risks triggering a price war they are unlikely to win.

Oligopoly Profit Maximization and the Supply Curve

Oligopoly has no single, well-defined supply curve. A supply curve shows quantity supplied at each price, independent of demand conditions. In oligopoly, the profit-maximizing quantity depends on the specific demand curve a firm faces, which itself depends on how rivals are expected to behave. Change the strategic assumption, and the same cost structure produces a different output decision.

Where a firm's relevant demand and marginal revenue curve can be identified, the profit-maximizing rule remains consistent: produce where MR = MC, then read price from the demand curve at that output. What changes across models is which demand curve applies.

High entry barriers allow oligopoly firms to earn economic profit in the long run. That profit is not permanent. Entry by new competitors, innovation, and shifts in strategic behavior among existing firms can erode a dominant position over time.

How to Choose the Right Oligopoly Model

Model selection depends on the assumption described in the question. Use this table to match the setup to the correct framework.

Identify the assumption first. Applying MR = MC before confirming which demand curve is relevant is the most common source of error in this topic.

Worked Strategy Example

Two streaming platforms, StreamCo and ViewNow, are the only providers in a small national market. Each must set its monthly price as either High (15)orLow(10). The payoff matrix below shows monthly profit in millions, with StreamCo's profit listed first in each cell.

Step 1: Find StreamCo's best response. If ViewNow plays High, StreamCo earns 12 from High or 14 from Low. StreamCo prefers Low. If ViewNow plays Low, StreamCo earns 4 from High or 8 from Low. StreamCo prefers Low. StreamCo's best response is Low regardless of ViewNow's choice.

Step 2: Find ViewNow's best response. If StreamCo plays High, ViewNow earns 12 from High or 14 from Low. ViewNow prefers Low. If StreamCo plays Low, ViewNow earns 4 from High or 8 from Low. ViewNow prefers Low. ViewNow's best response is also Low regardless of StreamCo's choice.

Step 3: Identify the Nash equilibrium. Both firms choosing Low is the Nash equilibrium. Neither firm can improve its own profit by switching strategy while the other holds Low fixed. This outcome pays each firm 8.

Step 4: Compare with the joint-profit-maximizing outcome. Both firms choosing High produces combined profit of 24 (12 + 12), higher than the 16 (8 + 8) combined profit at the Nash equilibrium. High-High is the collusive outcome.

Plain-English interpretation: Each firm has a private incentive to cut price no matter what the rival does, so both end up at Low-Low even though both would earn more at High-High. This is why collusion, if the firms could enforce it, would raise joint profit above the competitive Nash result. It also shows why cheating is tempting: if ViewNow trusts StreamCo to hold High, ViewNow earns 14 by secretly switching to Low.

Common Exam Traps

• Assuming every oligopoly follows kinked demand. Kinked demand applies only when the question describes rivals matching cuts but ignoring increases. Many oligopoly questions involve Cournot, Nash, or collusion assumptions instead.

• Using kinked demand to explain the original price. The model explains why an existing price stays fixed. It does not determine how that price was set in the first place.

• Confusing Cournot with price competition. Cournot firms choose quantity, not price. Mixing this up leads to applying the wrong reaction function or demand curve.

• Picking the highest joint-profit cell instead of the Nash equilibrium. A Nash equilibrium requires each firm to be playing its individual best response. The cell with the highest combined profit is only a Nash equilibrium if neither firm has an incentive to deviate from it alone.

• Assuming collusion is automatically stable. Every cartel member has an incentive to cheat. Collusion often breaks down without enforcement mechanisms or credible retaliation.

• Treating oligopoly as having a standard supply curve. Output depends on the strategic model in use, not on price and marginal cost alone. There is no single supply curve independent of demand and rival behavior.

• Applying MR = MC before identifying the relevant demand. Confirm which model applies and which demand curve is relevant before setting MR equal to MC. Using the wrong demand curve produces the wrong price and output.

Practice Question

Two airlines, JetPeak and SkyLow, are the only carriers on a regional route. Each airline can price a one-way ticket as either $200 or $150. Industry data shows that if both airlines choose $200, each earns $6 million in monthly profit. If one airline charges $200 while the other charges $150, the higher-priced airline earns $2 million and the lower-priced airline earns $9 million. If both airlines choose $150, each earns $4 million.

What is the Nash equilibrium in this pricing game?

1. Both airlines charge $200, since this maximizes combined industry profit.

2. Both airlines charge $150, since each airline's best response is to price low regardless of the rival's choice.

3. One airline charges $200 while the other charges $150, since this outcome rewards the lower-priced airline.

FAQs About Oligopoly