1. A Few (too few) Competitors May Lead to Monopoly-like Behavior
Ch Oligopoly
A Few (too few) Competitors
May Lead to Monopoly-like Behavior

2. What is an Oligopoly?
market in which the industry is dominated by a small number of sellers
Derived from the Greek for few sellers.
Since there are few participants, each oligopolist (firm) is aware of the actions of the others
decisions of one firm influence, and are influenced by the decisions of other firms
i.e., firms’ behave strategically taking into account the likely responses of the other market participants (game theory)

3. Oligopoly
Oligopoly markets are more concentrated than monopolistically competitive markets, but less concentrated than monopolies.
Perfect Competition
Monopoly
Monopolistic Competition
Oligopoly

4. Oligopolies - Characteristics
Oligopoly Is Widespread
Businesses that are part of an oligopoly share some common characteristics:
They are less concentrated than in a monopoly, but more concentrated than in a competitive system.
There is still competition within an oligopoly, as in the case of airlines. Airlines match competitor’s air fares when sharing the same routes. Also, automobile companies compete in the fall as the new models come out. One will reduce financing rates and the others will follow suit.   
The businesses offer an identical product or services.
This creates a high amount of interdependence which encourages competition in non price-related areas, like advertising and packaging. The tobacco companies, soft drink companies, and airlines are examples of an imperfect oligopoly.
Industries which are examples of oligopolies include:
Steel industry
Aluminum
Film
Television
Cell phone
Gas
There are:
Four music companies control 80% of the market - Universal Music Group, Sony Music Entertainment, Warner Music Group and EMI Group
Six major book publishers - Random House, Pearson, Hachette, HarperCollins, Simon & Schuster and Holtzbrinck
Four breakfast cereal manufacturers - Kellogg, General Mills, Post and Quaker
Two major producers in the beer industry - Anheuser-Busch and MillerCoors
Two major providers in the healthcare insurance market - Anthem and Kaiser Permanente
Pros and Cons
Pro: Prices in an oligopoly are usually lower than in a monopoly, but higher than it would be in a competitive market.
Pro: Prices tend to remain stable because if one company lowers the price too much, then the others will do the same. The result lowers the profit margin for all the companies, but is great for the consumer. 
Con: Output would be less than in a competitive market and more than in a monopoly.  Most competition between companies in an oligopoly is by means of research and development (or innovation), location, packaging, marketing, and the production of a product that is slightly different than the other company makes.
Con: Major barriers keep companies from joining oligopolies. The major barriers are economies of scale, access to technology, patents, and actions of the businesses in the oligopoly. Barriers can also be imposed by the government, such as limiting the number of licenses that are issued.
Con: Oligopolies develop in industries that require a large sum of money to start.  Existing companies in oligopolies discourage new companies because of exclusive access to resources or patented processes, cost advantages as the result of mass production, and the cost of convincing consumers to try a new product.
Lastly, companies in oligopolies establish exclusive dealerships, have agreements to get lower prices from suppliers, and lower prices with the intention of keeping new companies out.
Read more at
Oligopolies - Characteristics
Businesses that are part of an oligopoly share some common characteristics:
They are less concentrated than in a monopoly, but more concentrated than in a competitive system.
There is still competition within an oligopoly, as in the case of airlines. Airlines match competitor’s air fares when sharing the same routes. Also, automobile companies compete in the fall as the new models come out. One will reduce financing rates and the others will follow suit.   
The businesses offer an identical product or services.
This creates a high amount of interdependence which encourages competition in non price- related areas, like advertising and packaging. The tobacco companies, soft drink companies, and airlines are examples of an imperfect oligopoly.

5. Oligopolistic Industries - Examples
Industries which are examples of oligopolies include:
Steel industry
Aluminum
Film
Television
Cell phone
Gas

6. Examples of Oligopoly
Four music companies control 80% of the market - Universal Music Group, Sony Music Entertainment, Warner Music Group and EMI Group
Six major book publishers - Random House, Pearson, Hachette, HarperCollins, Simon & Schuster and Holtzbrinck
Four breakfast cereal manufacturers - Kellogg, General Mills, Post and Quaker
Two major producers in the beer industry - Anheuser-Busch and MillerCoors
Two major providers in the healthcare insurance market - Anthem and Kaiser Permanente

7. Pros and Cons of Oligopolies
Pro: Prices in an oligopoly are usually lower than in a monopoly, but higher than it would be in a competitive market.
Pro: Prices tend to remain stable because if one company lowers the price too much, then the others will do the same. The result lowers the profit margin for all the companies, but is great for the consumer

8. Pros and Cons of Oligopolies
Con: Output would be less than in a competitive market and more than in a monopoly.  Most competition between companies in an oligopoly is by means of research and development (or innovation), location, packaging, marketing, and the production of a product that is slightly different than the other company makes.
Con: Major barriers keep companies from joining oligopolies. The major barriers are economies of scale, access to technology, patents, and actions of the businesses in the oligopoly. Barriers can also be imposed by the government, such as limiting the number of licenses that are issued.
Con: Oligopolies develop in industries that require a large sum of money to start.  Existing companies in oligopolies discourage new companies because of exclusive access to resources or patented processes, cost advantages as the result of mass production, and the cost of convincing consumers to try a new product.
Lastly, companies in oligopolies establish exclusive dealerships, have agreements to get lower prices from suppliers, and lower prices with the intention of keeping new companies out.

9. How do we tell?
Market concentration refers to the size and distribution of firm market shares and the number of firms in the market.
Economists use two measures of industry concentration:
Four-firm Concentration Ratio
The Herfindahl-Hirschman Index

10. Four-Firm Concentration Ratio
The four-firm concentration ratio (CR4) measures market concentration by adding the market shares of the four largest firms in an industry.
If CR4 > 60, then the market is likely to be oligopolistic.

11. The Herfindahl-Hirschman Index
The Herfindahl-Hirschman index (HHI) is found by summing the squares of the market shares of all firms in an industry.
Advantages over the CR4 measure:
Captures changes in market shares
Uses data on all firms
HHI > > Potentially Too Concentrated

12. Figure 12.11 Four-Firm Concentration Ratio (CR4) for Selected Industries in 1997

13. Non-competitive Oligopolies
Non-competitive/collusive behavior (cooperative oligopolies)
Cartels: firms may collude to raise prices and restrict production in the same way as a monopoly. Where there is a formal agreement for such collusion, this is known as a cartel.
Dominant Firm/Price Leader:
collude in an attempt to stabilize unstable markets, so as to reduce the risks inherent in these markets for investment and product development.
does not require formal agreement
although for the act to be illegal there must be a real communication between companies
for example, in some industries, there may be an acknowledged market leader which informally sets prices to which other producers respond, known as price leadership.
Stackleberg price-leader model

14. Duopoly Equilibrium in a Centralized Cartel

15. Cartel Pricing Tactic Reduce Qs to monopoly levels in order to:
a) obtain a higher price
b) earn monopoly rents

16. Competition Versus Cartel
(a) Firm
(b) Market
Price, p ,
Price, p ,
$ per unit
$ per unit M C S e m p p m AC m p p e c c c MC MC m m
Market demand MR q q q * Q Q m c m c
Quantity, q
, Units
Quantity, Q
, Units
per year
per year
Source: Jeffrey M. Perloff, Microeconomics, 3rd Ed., 2004, p. 435

17. Strategic Behavior Perfect Competition
Only strategy is to reduce costs
Price-taker => output decisions do not affect market price
cross-price elasticity = -1 (perfect substitutes)
Own-price = -∞
Monopoly
Price-Searcher: output decision determines price
Cross-price = 0 (no substitutes)
Own-price: >= |1|
Oligopoly
Cross-price elasticity near -1
Own-price elasticity > |1|
Will have to take into account actions of other similar firms when making output/pricing decisions
Much more strategy

18. Oligopoly Behavior Cooperative Oligopoly Non-cooperative Oligopolies
Cartels
Agree to collude; act/price like a single firm monoploist
Price leadership (Stackleberg leader)
Dominant firm establishes the price; other firms react to “leader”
Non-cooperative Oligopolies
Sticky prices (kinked demand curve)
Sticky upward
Nash equilibrium
Characterized by stable prices
Perfect competition
Completely rivalarous

19. Cooperative Oligopolies
Cartels (highly cooperative)
Firms act as single-firm monopolist
Stackelberg Price Leader (passive cooperation)
- leader firm moves first and then the follower firms move sequentially
Stackelberg leader is sometimes referred to as the Market Leader.