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```Chapter 12
Oligopoly
Oligopoly – Characteristics
 Small number of firms
 Product differentiation may or may not
exist
 Barriers to entry
Chapter 12
2
Oligopoly – Equilibrium
 Defining Equilibrium
Firms are doing the best they can and have
no incentive to change their output or price
 Nash Equilibrium
Each firm is doing the best it can given what
its competitors are doing.
Chapter 12
3
Duopoly
 The Cournot Model
Oligopoly model in which firms produce a
homogeneous good, each firm treats the
output of its competitors as fixed, and all
firms decide simultaneously how much to
produce
Firm will adjust its output based on what it
thinks the other firm will produce
Chapter 12
4
Firm 1’s Output Decision
P1
Firm 1 and market demand curve,
D1(0), if Firm 2 produces nothing.
D1(0)
If Firm 1 thinks Firm 2 will produce
50 units, its demand curve is
shifted to the left by this amount.
MR1(0)
D1(75)
If Firm 1 thinks Firm 2 will produce
75 units, its demand curve is
shifted to the left by this amount.
MR1(75)
MC1
MR1(50)
12.5 25
D1(50)
50
Chapter 12
Q1
5
Oligopoly
 The Reaction Curve
The relationship between a firm’s profitmaximizing output and the amount it thinks
its competitor will produce.
A firm’s profit-maximizing output is a
decreasing schedule of the expected output
of Firm 2.
Chapter 12
6
Reaction Curves and Cournot
Equilibrium
Q1
Firm 1’s reaction curve shows how much it
will produce as a function of how much
it thinks Firm 2 will produce. The x’s
correspond to the previous model.
100
75
Firm 2’s Reaction
Curve Q*2(Q2)
Firm 2’s reaction curve shows how much it
will produce as a function of how much
it thinks Firm 1 will produce.
50 x
25
x
Firm 1’s Reaction
Curve Q*1(Q2)
25
50
x
75
Chapter 12
x
100
Q2
7
Reaction Curves and Cournot
Equilibrium
Q1
In Cournot equilibrium, each
firm correctly assumes how
much its competitors will
produce and thereby
maximize its own profits.
100
75
Firm 2’s Reaction
Curve Q*2(Q2)
50 x
25
Cournot
Equilibrium
x
Firm 1’s Reaction
Curve Q*1(Q2)
25
50
x
75
Chapter 12
x
100
Q2
8
Cournot Equilibrium
 Each firms reaction curve tells it how
much to produce given the output of its
competitor.
 Equilibrium in the Cournot model, in
which each firm correctly assumes how
much its competitor will produce and sets
its own production level accordingly.
Chapter 12
9
Oligopoly
 Cournot equilibrium is an example of a
Nash equilibrium (Cournot-Nash
Equilibrium)
 The Cournot equilibrium says nothing
process
Chapter 12
10
Oligopoly: Example
 An Example of the Cournot Equilibrium
Two firms face linear market demand curve
Market demand is P = 30 - Q
Q is total production of both firms:
Q = Q1 + Q2
Both firms have MC1 = MC2 = 0
Chapter 12
11
Oligopoly Example
 Firm 1’s Reaction Curve  MR=MC
Total Revenue : R1  PQ1  (30  Q)Q1
 30Q1  (Q1  Q2 )Q1
 30Q1  Q12  Q2Q1
Chapter 12
12
Oligopoly Example
 An Example of the Cournot Equilibrium
MR1  R1 Q1  30  2Q1  Q2
MR1  0  MC 1
Firm 1' s Reaction Curve
Q1  15  1 2 Q2
Firm 2' s Reaction Curve
Q2  15  1 2 Q1
Chapter 12
13
Oligopoly Example
 An Example of the Cournot Equilibrium
Cournot Equilibrium : Q1  Q2
15  1 2(15  1 2Q1 )  10
Q  Q1  Q2  20
P  30  Q  10
Chapter 12
14
Duopoly Example
Q1
30
Firm 2’s
Reaction Curve
The demand curve is P = 30 - Q and
both firms have 0 marginal cost.
Cournot Equilibrium
15
10
Firm 1’s
Reaction Curve
10
15
Chapter 12
30
Q2
15
Oligopoly Example
 Profit Maximization with Collusion
R  PQ  (30  Q)Q  30Q  Q
MR  R Q  30  2Q
MR  0 when Q  15 and MR  MC
2
Chapter 12
16
Profit Max with Collusion
 Contract Curve
Q1 + Q2 = 15
 Shows
all pairs of output Q1 and Q2 that
maximizes total profits
Q1 = Q2 = 7.5
 Less
output and higher profits than the Cournot
equilibrium
Chapter 12
17
Duopoly Example
Q1
30
Firm 2’s
Reaction Curve
For the firm, collusion is the best
outcome followed by the Cournot
Equilibrium and then the
competitive equilibrium
Competitive Equilibrium (P = MC; Profit = 0)
15
Cournot Equilibrium
Collusive Equilibrium
10
7.5
Firm 1’s
Reaction Curve
Collusion
Curve
7.5 10
15
Chapter 12
30
Q2
18
Stackelberg Model
 Oligopoly model in which one firm sets its
output before other firms do.
 Assumptions
One firm can set output first
MC = 0
Market demand is P = 30 - Q where Q is total
output
Firm 1 sets output first and Firm 2 then
makes an output decision seeing Firm 1
output
Chapter 12
19
Stackelberg Model
 Firm 1
Must consider the reaction of Firm 2
 Firm 2
Takes Firm 1’s output as fixed and therefore
determines output with the Cournot reaction
curve: Q2 = 15 - ½(Q1)
Chapter 12
20
Stackelberg Model
 Firm 1
Choose Q1 so that:
MR  MC  0
R1  PQ1  30Q1 - Q - Q2Q1
2
1
Firm 1 knows that firm 2 will choose output
based on its reaction curve. We can use firm
2’s reaction curve as Q2
Chapter 12
21
Stackelberg Model
 Using Firm 2’s Reaction Curve for Q2:
R1  30Q1  Q12  Q1 (15  1 2Q1 )
 15Q1  1 2 Q
2
1
MR1  R1 Q1  15  Q1
MR  0 : Q1  15 and Q2  7.5
Chapter 12
22
Stackelberg Model
 Conclusion
Going first gives firm 1 the advantage
Firm 1’s output is twice as large as firm 2’s
Firm 1’s profit is twice as large as firm 2’s
 Going first allows firm 1 to produce a
large quantity. Firm 2 must take that into
account and produce less unless it wants
to reduce profits for everyone
Chapter 12
23
Competition Versus Collusion:
The Prisoners’ Dilemma
 Nash equilibrium is a noncooperative
equilibrium: each firm makes decision
that gives greatest profit, given actions of
competitors
Chapter 12
24
Competition Versus Collusion:
The Prisoners’ Dilemma
 The Prisoners’ Dilemma illustrates the
problem that oligopolistic firms face.
Two prisoners have been accused of
collaborating in a crime.
They are in separate jail cells and cannot
communicate.
Each has been asked to confess to the crime.
Chapter 12
25
Payoff Matrix for Prisoners’
Dilemma
Prisoner B
Confess
Confess
Prisoner A
Don’t
confess
-6, -6
Don’t confess
0, -10
Would you choose to confess?
-10, 0
Chapter 12
-2, -2
26
Oligopolistic Markets

1.
2.
3.
Conclusions
Collusion will lead to greater profits
Explicit and implicit collusion is possible
Once collusion exists, the profit motive
to break and lower price is significant
Chapter 12
27
 The Dominant Firm Model
In some oligopolistic markets, one large firm
has a major share of total sales, and a group
of smaller firms supplies the remainder of the
market.
The large firm might then act as the
dominant firm, setting a price that maximizes
its own profits.
Chapter 12
28
Price Setting by a Dominant
Firm
Price
SF
D
The dominant firm’s demand
curve is the difference between
market demand (D) and the supply
of the fringe firms (SF).
P1
MCD
P*
DD
P2
QF QD
QT
MRD
Chapter 12
At this price, fringe firms
sell QF, so that total
sales are QT.
Quantity
29
```
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