1. Market Institutions: Oligopoly
Topic 2 – Part I
Market Institutions: Oligopoly

2. Topic Outline Oligopoly Characterization Stackelberg Model
Cournot Model
Cartel Formation and Stability
Bertrand Model

3. Oligopoly
Often there are a number of competitors in the market but not so many as to regard each of them as having a negligible effect on price. This is the market structure known as oligopoly
Oligopoly industry is characterized by encompassing a small number of firms
We will restrict our analysis to the case of two firms (duopoly) that produce identical products

4. Choosing a Strategy
If there are two firms in the market producing a homogeneous product, there are 4 variables of interest: price that each firm charges and quantity that each firm produces
When one firm makes its choices of price and quantity, it may already know the choices made by the other firm. The strategic interaction form a sequential game
If one firm gets to set its price before the other firm, we call it the price leader and the other firm the price follower
Similarly, one firm may get to choose its quantity first, in which case it is a quantity leader and the other firm is a quantity follower

5. Choosing a Strategy (cont.)
When one firm makes its choices of price and quantity, it may not know the choices made by the other firm. In this case, it has to guess about the other firm’s choices in order to make sensible decisions. The strategic interaction form a simultaneous game
Therefore, the competitive strategic interaction between these two firms gives 4 possible scenarios:
Quantity leadership  Stackelberg Model
Price leadership
Simultaneous quantity setting  Cournot Model
Simultaneous price setting  Bertrand Model

6. Choosing a Strategy (cont.)
Another form of interaction is when, instead of the firms competing against each other, they may be able to collude
In this case, the two firms can jointly agree to set price and quantity that maximizes the sum of their profits
This collusion among oligopolistic firms is called Cartel

7. Quantity Leadership: Stackelberg Model
Suppose there are two firms in the market (duopoly)
One firm (Firm1) choose a level of output before the other firm (Firm 2)
After observing the decision of Firm 1, Firm 2 decides a level of output
This model is used to describe industries in which there is a dominant firm or natural leader called the Stackelberg leader

8. Quantity Leadership: Stackelberg Model (cont.)
This strategic situation can be modeled using an extensive-form game-theoretic representation
The SPNE of the game will provide the information about the Stackelberg equilibrium and equilibrium payoffs for both firms (profits)

9. Model Setup
Suppose firm 1 is the leader and that it chooses to produce a quantity y1
Firm 2 responds by choosing quantity y2
Each firm knows that the equilibrium price in the market depends on the total output produced
What output should the leader choose to maximize its profits? The answer depends on how the leader thinks that the follower will react to its choice
The leader should expect that the follower will attempt to maximize profits as well, given a choice made by the leader
Therefore, the leader should consider the follower’s profit-maximization problem in order to make a sensible decision about its own production

10. Model Solution
Start by the end of the game: evaluate the follower’s maximization problem, taking as predetermined the level of output chosen by the leader:
The follower chooses y2 such that Π2 (y1, y2) is maximized
You will find y2 = f(y1), the reaction function for the follower
Solve the leader’s optimization problem, subject to the reaction of the follower
The leader chooses y1 such Π1 (y1, y2) is maximized subject to y2 = f(y1), i.e., max Π1 (y1, f(y1))

11. Simultaneous Quantity Setting: Cournot Model
Two firms are simultaneously trying to decide what quantity to produce. Here each firm has to forecast what the other firm’s output will be in order to make a sensible decision itself
Given its forecast, each firm chooses a profit-maximizing output for itself
We seek an equilibrium in forecasts: a situation where each firm finds its beliefs about the other firm to be confirmed, and in which each firm’s decision is best response to the strategy they believe the opponent will choose

12. Model Setup
Assume that firm 1 expects that firm 2 will produce y2e units of output. The superscript “e” stands for “expected” output
If firm 1 decides to produce y1 units of output, it expects that the total output produced will be Y = y1 + y2e
This output will yield a market price p(Y) = p (y1 + y2e)

13. Model Solution
The profit-maximizing problem of firm 1: max profits 1 by choosing y1, taking as given y2e
Find reaction function for firm 1 to its beliefs about level of output of firm 2
The profit-maximizing problem of firm 2: max profits 2 by choosing y2, taking as given y1e
Find reaction function for firm 2 to its beliefs about level of output of firm 1

14. Model Solution (cont.)
We are searching for an equilibrium (y1, y2) where y1e = y1* and y2e = y2*
Combine both reaction functions to obtain optimal
(y1*, y2*) such that
y1* = f1 (y2*)
y2* = f2(y1*)

15. Model Solution (cont.) In a Cournot equilibrium
Each firm is maximizing its profits, given its beliefs about the other firm’s output choice
Those beliefs are confirmed in equilibrium: each firm optimally chooses to produce the amount of output that the other firm expects it to produce
Neither firm will find it profitable to change its output once it discovers the choice actually made by the other firm. Therefore, the Cournot equilibrium is an Nash-equilibrium