Oligopoly

oligopolisticoligopoliesoligopolistsoligopoly theorycorporate oligopoliesDuopolyoligopolistdominated by a very small number of firmsmonopolisticnotary oligopoly
An oligopoly is a market form wherein a market or industry is dominated by a small number of large sellers (oligopolists).wikipedia
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Monopoly

monopoliesmonopolisticmonopolist
In some situations, particular companies may employ restrictive trade practices (collusion, market sharing etc.) in order to inflate prices and restrict production in much the same way that a monopoly does.
This contrasts with a monopsony which relates to a single entity's control of a market to purchase a good or service, and with oligopoly which consists of a few sellers dominating a market.

Tacit collusion

price leadershiptacitly colludeprice leader
There does not have to be a formal agreement for collusion to take place (although for the act to be illegal there must be actual 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.
Oligopolists usually try not to engage in price cutting, excessive advertising or other forms of competition.

Concentration ratio

concentrationmarket concentration
As a quantitative description of oligopoly, the four-firm concentration ratio is often utilized.
Concentration ratios are usually used to show the extent of market control of the largest firms in the industry and to illustrate the degree to which an industry is oligopolistic.

Duopoly

duopoliesduopolistic markettwin-duopolistic
A duopoly (from Greek δύο, duo (two) + πωλεῖν, polein (to sell)) is a type of oligopoly where two firms have dominant or exclusive control over a market.

Collusion

colludingcolludedcollude
In some situations, particular companies may employ restrictive trade practices (collusion, market sharing etc.) in order to inflate prices and restrict production in much the same way that a monopoly does.
Collusion most often takes place within the market structure of oligopoly, where the decision of a few firms to collude can significantly impact the market as a whole.

Kinked demand

kinked demand curvekinked demand curve model
Some of the better-known models are the dominant firm model, the Cournot–Nash model, the Bertrand model and the kinked demand model.
The Kinked-Demand curve theory is an economic theory regarding oligopoly and monopolistic competition.

Competition

competitorcompetitionscompetitive
Oligopolistic competition can give rise to both wide-ranging and diverse outcomes.
The greater selection typically causes lower prices for the products, compared to what the price would be if there was no competition (monopoly) or little competition (oligopoly).

Market structure

market formMarket formsnon-competitive markets
An oligopoly is a market form wherein a market or industry is dominated by a small number of large sellers (oligopolists).
The imperfectly competitive structure is quite identical to the realistic market conditions where some monopolistic competitors, monopolists, oligopolists, and duopolists exist and dominate the market conditions.

Aircraft tire

Aircraft tiresaviation tiresList of aircraft tire companies
The aircraft tire manufacturing industry is dominated by a four firm oligopoly that controls 85% of market share.

Game theory

gamegame theoristgame theoretic
According to game theory, the decisions of one firm therefore influence and are influenced by decisions of other firms.
Applications include a wide array of economic phenomena and approaches, such as auctions, bargaining, mergers & acquisitions pricing, fair division, duopolies, oligopolies, social network formation, agent-based computational economics, general equilibrium, mechanism design, and voting systems; and across such broad areas as experimental economics, behavioral economics, information economics, industrial organization, and political economy.

Perfect competition

perfectly competitiveperfect marketimperfect market
This could lead to an efficient outcome approaching perfect competition.
Economic profit is, however, much more prevalent in uncompetitive markets such as in a perfect monopoly or oligopoly situation.

Cartel

cartelsprice fixing cartelTrusts
Whenever there is a formal agreement for such collusion, between companies that usually compete with one another, this practice is known as a cartel.

Antoine Augustin Cournot

CournotAugustin CournotAntoine Augustine Cournot
The Cournot–Nash model is the simplest oligopoly model.
In the field of economics he is best known for his work in the field of oligopoly theory—Cournot competition which is named after him.

Joseph Bertrand

Joseph Louis François BertrandBertrandCalcul des probabilités
In the field of economics he reviewed the work on oligopoly theory, specifically the Cournot Competition Model (1838) of French mathematician Antoine Augustin Cournot.

Barriers to entry

barrier to entryentry barrierbarriers
In industrialized economies, barriers to entry have resulted in oligopolies forming in many sectors, with unprecedented levels of competition fueled by increasing globalization.

Monopolistic competition

monopolistically competitivemonopolisticmonopolistic competitors
Classical economic theory assumes that a profit-maximizing producer with some market power (either due to oligopoly or monopolistic competition) will set marginal costs equal to marginal revenue.

Concentration of media ownership

media concentrationmedia consolidationmedia ownership
Contemporary research demonstrates increasing levels of consolidation, with many media industries already highly concentrated and dominated by a very small number of firms.

Credit rating agency

credit rating agenciesrating agencyrating agencies
Agencies are sometimes accused of being oligopolists, because barriers to market entry are high and rating agency business is itself reputation-based (and the finance industry pays little attention to a rating that is not widely recognized).

Conjectural variation

conjecture of Nash
In oligopoly theory, conjectural variation is the belief that one firm has an idea about the way its competitors may react if it varies its output or price.

Oligopsony

It contrasts with an oligopoly, where there are many buyers but few sellers.

Swing producer

swing oil producer
Swing producer is a supplier or a close oligopolistic group of suppliers of any commodity, controlling its global deposits and possessing large spare production capacity.

Price war

price competitionfare warcompete on price
However, even a large price decrease will gain only a few customers because such an action will begin a price war with other firms.
In oligopoly markets prices can become 'sticky' because if the price rises, competitors will not follow the rise.

Imperfect competition

imperfectly competitiveanti-competitiveimperfect
In an oligopoly, firms operate under imperfect competition.

Prisoner's dilemma

iterated prisoner's dilemmaprisoner’s dilemmaprisoners' dilemma
The prisoner's dilemma has been called the E. coli of social psychology, and it has been used widely to research various topics such as oligopolistic competition and collective action to produce a collective good.