Unit 7: Oligopoly

Oligopoly is a market structure dominated by a small number of interdependent sellers, standing between monopoly (one seller) and monopolistic competition (many sellers). Because each firm is large relative to the market, its price and output decisions provoke reactions from rivals, so no firm can plan in isolation. This mutual interdependence is the single feature every model in this unit returns to.

Defining characteristics of oligopoly:

• Few sellers, many buyers: A handful of firms (e.g. 2 to 10) supply the bulk of output; a duopoly is the two-firm special case.
• Interdependence: Each firm's optimal action depends on rivals' expected responses, so demand facing a firm is indeterminate without assumptions about reactions.
• Barriers to entry: Economies of scale, patents, capital requirements and brand loyalty keep new entrants out, sustaining supernormal profit in the long run.
• Product type: Homogeneous (pure oligopoly, e.g. steel, cement, aluminium) or differentiated (imperfect oligopoly, e.g. cars, smartphones).
• Indeterminate demand curve: Because a rival may match or ignore a price change, a firm cannot draw a single definite demand curve.
• Price rigidity: Prices tend to stay sticky for long periods, explained by the kinked demand curve where rivals match price cuts but not price rises.
• Non-price competition: Firms prefer advertising, packaging, after-sales service and product variation over price war, which is mutually destructive.

II. Meaning and Sources — Why Few Firms Come to Dominate

This section fixes what oligopoly is and why markets consolidate into a small number of firms.

A. Meaning

Oligopoly is defined by the smallness of numbers combined with strategic interdependence.

• Literal origin: From Greek oligoi (few) and polein (to sell) — "competition among the few."
• Working definition: A market in which a few firms control the entire supply, and each firm's share is large enough that its actions measurably affect rivals' sales and prices.
• Concentration measure: Captured by the concentration ratio, e.g. CR4, the combined market share of the four largest firms.

CR4 = (S1 + S2 + S3 + S4) / Total market sales × 100

• Symbols: S1…S4 = sales of the four largest firms; a CR4 above roughly 60% signals a tight oligopoly.
  • Reaction function: Each firm forms a conjecture about how rivals will respond; the demand it perceives shifts with that conjecture, which is why equilibrium requires game-theoretic reasoning.
  • Duopoly: The limiting case of two sellers (analysed in the Cournot and Bertrand models), where interdependence is at its starkest.

B. Sources

The syllabus asks why the number of sellers stays small; the sources are the barriers that block entry and encourage merger.

• Economies of scale: Long-run average cost keeps falling until output is a large fraction of total demand, so only a few plants of efficient size can survive — typical in automobiles and cement.
• Control over inputs / raw materials: Ownership of key resources (e.g. bauxite for aluminium) prevents rivals from producing at competitive cost.
• Patents and technology: Exclusive rights to a process or design shut out imitators for the patent's life.
• Heavy capital requirement: The large fixed investment needed for plants, distribution and R&D deters small entrants.
• Mergers and takeovers: Firms combine to gain market power, directly reducing the number of independent sellers.
• Brand loyalty and advertising: Established goodwill built through sustained promotion forces entrants to spend heavily merely to be noticed.
• Legal and licensing restrictions: Government licences, quotas or franchises can legally cap the number of producers.

III. Cartelization under Oligopoly — Collusion to Act as a Monopoly

A cartel is a formal agreement among oligopolists to coordinate price and output so the group jointly captures monopoly profit. It converts interdependence from a threat into a shared advantage.

A. Nature and objective

• Definition: A cartel is an association of independent firms that centralises decisions on price, output or market sharing while firms retain separate ownership.
• Goal — joint profit maximisation: The cartel behaves like a multi-plant monopolist, choosing total output where combined marginal revenue equals aggregate marginal cost.

Joint profit max:  MR(market) = ΣMCi

• Symbols: MR(market) = marginal revenue on the cartel's total output; ΣMCi = horizontal summation of member firms' marginal cost curves.
  • Quota allocation: Total profit-maximising output is split among members, ideally so each firm produces where its own MC equals the common cartel marginal cost, minimising total cost.
  • OPEC illustration: The Organization of the Petroleum Exporting Countries sets national production quotas to hold up crude prices — a real-world price-and-output cartel.

B. Types and working

• Centralised (perfect) cartel: A central board sets a single price and allocates output quotas; profits are pooled and redistributed. Yields the pure monopoly outcome.
• Market-sharing cartel: Members agree on non-price division of the market, either by:
  • Territory: Each firm is assigned exclusive regions.
  • Quota: Each firm receives a fixed percentage of total sales.
• Loose / price cartel: Members fix only a common price and then compete on output and non-price terms.

Worked illustration of quota logic: Suppose the cartel's profit-maximising output is 100 units. Firm A (MC = 20 at the margin) and Firm B (MC = 20 at the margin) share output so that both operate at the same marginal cost of 20; if A is lower-cost it gets the larger quota, cutting the group's total production cost.

C. Instability and limitations

• Incentive to cheat: At the cartel price, each member faces a highly elastic firm demand and can raise profit by secretly cutting price and expanding sales — the dominant temptation that undermines every cartel.
• Detection lag: Secret price cuts spread before the board can react, triggering the very price war the cartel was meant to avoid.
• Entry of outsiders: High cartel profits attract non-member firms whose output erodes the agreed price.
• Cost differences: Widely differing cost curves make an agreed uniform price and quota split hard to negotiate.
• Legal prohibition: Anti-trust and competition laws (in many countries) make explicit cartels illegal, forcing collusion underground and raising its cost.
• Demand fluctuations: Uncertain market demand makes the joint-profit-maximising price a moving target, straining agreement.

IV. Price Leadership under Oligopoly — Tacit Coordination Without a Formal Pact

Price leadership is a form of implicit collusion in which one firm sets the price and the others follow, achieving coordination without an illegal formal agreement. It resolves interdependence by convention rather than contract.

A. Meaning and mechanism

• Definition: One firm — the leader — announces a price and the remaining firms (followers) adopt it as their own.
• Why it arises: It avoids ruinous price wars and the legal exposure of a cartel while still stabilising the market price.
• Follower behaviour: Followers accept the leader's price as given and behave like price-takers, adjusting only their output.

B. Forms of price leadership

The leader emerges for different reasons, giving distinct models.

1. Dominant-firm price leadership: One large firm supplies most of the market alongside a competitive fringe of small firms.
   • Fringe first: Small firms sell all they wish at the leader's price, acting as price-takers.
   • Leader's demand: The dominant firm faces the market demand minus the fringe supply, i.e. its demand is the residual.

Dd = D(P) − Sf(P)

• Symbols: Dd = dominant firm's demand; D(P) = total market demand; Sf(P) = combined supply of the fringe at price P.
• Leader's rule: The dominant firm sets output where its own MR = MC on this residual demand, and the resulting price becomes the market price.

2. Barometric price leadership: A firm respected for reading market conditions — not necessarily the largest — initiates price changes that others follow because its judgement is trusted.
   • Basis: Leadership rests on information and forecasting skill, so the leader can rotate over time.

• Low-cost (efficient-firm) leadership: A related form in which the firm with the lowest cost sets a price the higher-cost rivals must accept to avoid being undercut.

C. Conditions and limitations

• Requires similar products: Followers accept the leader's price only when goods are close substitutes.
• Recognised leader: There must be tacit acceptance of who leads; disputed leadership breaks the arrangement.
• Follower discontent: If the leader sets a price too high, low-cost followers gain by shading it, weakening the leader's control.
• Threat of entry and non-price competition: A comfortable leader price invites new entrants and diverts rivalry into advertising and quality.
• Rigidity: Because changes are initiated only by the leader, prices adjust slowly to shifting demand and cost, reinforcing the price stickiness characteristic of oligopoly.

Cartelization and price leadership are thus two routes to the same end — dampening the destructive interdependence of oligopoly — one through explicit agreement and pooled decision-making, the other through tacit convention centred on a single price-setter.