CHAPTER 15: OLIGOPOLY
What Is Oligopoly?
Oligopoly is a market structure in which
Natural or legal barriers prevent the entry of new firms.
A small number of firms compete.
Barriers to Entry
Either natural or legal barriers to entry can create oligopoly.
Figure 15.1 shows two oligopoly situations.
In part (a), there is a natural duopoly—a market with two firms.
In part (b), there is a natural oligopoly market with three firms.
A legal oligopoly might arise even where the demand and costs leave room for a
larger number of firms.
Small Number of Firms
Because an oligopoly market has a small number of firms, the firms are
interdependent and face a temptation to cooperate.
Interdependence: With a small number of firms, each firm’s profit depends
on every firm’s actions.
Cartel: A cartel and is an illegal group of firms acting together to limit output, raise
price, and increase profit.
Firms in oligopoly face the temptation to form a cartel, but aside from being
illegal, cartels often break down. Two Traditional Oligopoly Models
The Kinked Demand Curve Model
In the kinked demand curve model of oligopoly, each firm believes that if it raises
its price, its competitors will not follow, but if it lowers its price all of its
competitors will follow.
Figure 15.2 shows the kinked demand curve model.
The firm believes that the demand for its product has a kink at the current price and
Above the kink, demand is relatively elastic because all other firm’s prices remain
Below the kink, demand is relatively inelastic because all other firm’s prices change
in line with the price of the firm shown in the figure.
The kink in the demand curve means that the MR curve is discontinuous at the
current quantity—shown by that gap AB in the figure The next diagram helps to envisage why the kink in the demand curve puts a break
in the marginal revenue curve.
Fluctuations in MC that remain within the discontinuous portion of the MR curve
leave the profit-maximizing quantity and price unchanged.
For example, if costs increased so that the MC curve shifted upward from MC0 to
MC1, the profit-maximizing price and quantity would not change The beliefs that generate the kinked demand curve are not always correct and firms
can figure out this fact.
If MC increases enough, all firms raise their prices and the kink vanishes.
A firm that bases its actions on wrong beliefs doesn’t maximize profit
Dominant Firm Oligopoly
In a dominant firm oligopoly, there is one large firm that has a significant
cost advantage over many other, smaller competing firms.
The large firm operates as a monopoly, setting its price and output to
maximize its profit.
The small firms act as perfect competitors, taking as given the market price
set by the dominant firm.
Figure 15.3 shows10 small firms in part (a). The demand curve, D, is the
market demand and the supply curve S10 is the supply of the 10 small firms The demand curve for the large firm’s output is the curve XD on the right.
The large firm can set the price and receives a marginal revenue that is less
than price along the curve MR.
The large firm maximizes profit by setting MR = MC. Let’s suppose that the
marginal cost curve is MC in the figure.
The profit-maximizing quantity for the large firm is 10 units. The price
charged is $1.00.
The small firms take this price and supply the rest of the quantity demanded
In the long run, such an industry might become a monopoly as the large firm
buys up the small firms and cuts costs Game Theory:
Game theory is a tool for studying strategic behaviour, which is behaviour that
takes into account the expected behaviour of others and the mutual recognition of
We will discuss the following games:
• Original prisoner’s dilemma
• Oligopoly game
• Battle of the sexes
• Game of Chicken
• Sequential games
The Prisoners’ Dilemma
The prisoners’ dilemma game illustrates the four features of a game.
Outcome Each is told that both are suspected of committing a more
If one of them confesses, he will get a 1-year sentence for
cooperating while his accomplice get a 10-year sentence for
If both confess to the more serious crime, each receives 3
years in jail for both crimes.
If neither confesses, each receives a 2-year sentence for the
minor crime only.
Strategies are all the possible actions of each player.
Art and Bob each have two possible actions:
1. Confess to the larger crime.
2. Deny having committed the larger crime.
With two players and two actions for each player, there are four possible
1. Both confess.
2. Both deny.
3. Art confesses and Bob denies.
4. Bob confesses and Art denies.
Each prisoner can work out what happens to hi