Bhanupratap Rathore

Backend & AI Engineer

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Oligopoly Markets

·4 min read
Micro Economics

Oligopoly Markets

Oligopoly markets are characterized by a few large firms. Their most striking feature is interdependence: each firm's decisions affect its rivals, creating uncertainty since no firm knows exactly how competitors will respond to its moves. Firms generally either collude to remove this uncertainty, or compete in its absence.

Non-Collusive Oligopoly Models

Sweezy's Kinked Demand Curve Hypothesis

Core Assumption: Firms face an asymmetric reaction from competitors when changing prices.

  • If a firm raises its price, rivals will not follow (hoping to steal customers) - demand is highly elastic above the current price.
  • If a firm lowers its price, rivals will match the cut to protect market share - demand is highly inelastic below the current price.

This asymmetry creates a kink in the demand curve at the prevailing market price.

Equilibrium & Rigidity: The sharp change in elasticity at the kink causes a vertical discontinuity (gap) in the Marginal Revenue (MR) curve directly beneath the kink. Because of this gap, fluctuations in Marginal Cost (MC) within that range don't change the profit-maximizing price or output. To the left of the kink, MR > MC (incentive to expand output up to the kink); to the right, MR < MC (disincentive to produce more). Consequently, prices tend to stay rigid at the kink point even as costs shift.

Cournot Model

Core Assumption: Firms compete on quantity, choosing output levels simultaneously. Each firm assumes its rival's output will stay constant when making its own decision.

Equilibrium: The intersection of the firms' reaction functions (each firm's profit-maximizing output given the rival's output). The resulting Nash equilibrium yields output higher than a monopoly but lower than perfect competition, with price in between.

Stackelberg Model

Core Assumption: An extension of Cournot with sequential moves. One firm (the Leader, usually the larger firm) chooses output first; the other (the Follower) chooses output after observing the leader's choice.

Equilibrium: The leader has a first-mover advantage - knowing the follower's reaction function, it factors this directly into its own profit-maximizing calculation. The leader produces more and the follower produces less than in the Cournot outcome.

Bertrand Model

Core Assumption: Firms compete on price, producing identical (homogeneous) products, choosing prices simultaneously. Consumers buy from whichever firm offers the lowest price.

Equilibrium: This leads to the Bertrand Paradox. Since products are identical, firms have a strong incentive to undercut each other, driving price down to marginal cost (P = MC). Firms earn zero economic profit - the same outcome as perfect competition, even with just two firms.

Collusive Oligopoly Models

Cartels

Core Assumption: Firms explicitly and formally agree to cooperate. Members coordinate to set a unified price, establish production quotas, and/or divide territories - effectively functioning as a single collective monopoly.

Equilibrium & Instability: The outcome mimics a monopoly - output is restricted to keep prices high. But because P > MC, individual members have a strong incentive to secretly exceed their quota. If enough members cheat, supply surges and price collapses back toward competitive levels.

Price Leadership

Core Assumption: A form of tacit (unspoken) collusion, avoiding formal agreements to sidestep antitrust laws. One benchmark firm acts as leader; when it adjusts price, other firms voluntarily follow.

Equilibrium: Price stays stable without explicit communication. If followers comply, the industry enjoys near-monopoly profits. If a rival refuses to follow a price hike, the leader may be forced to rescind it.

Dominant Firm Price Leadership

Core Assumption: The leader is the largest firm by market share. It sets price to maximize its own profit; smaller firms act as a competitive fringe.

Equilibrium: The dominant firm calculates residual demand (total demand minus what the fringe supplies) and sets price where its own MR = MC. Fringe firms act as price-takers, producing where their MC equals that price.

Low-Cost Price Leadership

Core Assumption: The leader is the most efficient firm (lowest costs), not necessarily the largest. It sets a price typically lower than what higher-cost rivals would prefer.

Equilibrium: The low-cost leader sets price where its own MR = MC. Higher-cost firms must accept this price since goods are close substitutes - undercutting it means losses, exceeding it means losing market share.

Barometric Firm Price Leadership

Core Assumption: The leader is chosen for its reliability in reading market conditions - typically an old, established firm with a track record of correctly interpreting shifts in demand, costs, or regulation.

Equilibrium: The barometric firm has no coercive power; when it changes price, this signals to others that fundamentals have shifted, and rivals follow out of trust rather than fear. If it misjudges the market, rivals won't follow and it must reverse the change.

Further Reading