Economics · Lesson 9

Market structures: perfect competition, monopoly & others

JAMBWAECNECO

What the syllabus asks

JAMB: Market structure: perfect competition, imperfect competition (monopoly, monopolistic competition, oligopoly); characteristics, price and output determination, equilibrium of the firm and industry in the short run and long run; price discrimination

WAEC: Market structures: perfect competition, monopoly, monopolistic competition, oligopoly and duopoly; features, short-run and long-run equilibrium of the firm; price discrimination; merits, demerits and control of monopoly

NECO: Market structures: perfect competition, monopoly, monopolistic competition, oligopoly and duopoly; features, short-run and long-run equilibrium of the firm; price discrimination; merits, demerits and control of monopoly

What you will learn

Explain the meaning of a market and the criteria used to classify market structures.
State the assumptions of perfect competition and derive the short-run and long-run equilibrium of the firm.
Explain the sources of monopoly power and find monopoly price and output using MC = MR.
State the conditions for, and types of, price discrimination.
Compare perfect competition with monopoly and assess methods of controlling monopoly.
Describe monopolistic competition and oligopoly, including excess capacity, collusion and the kinked demand curve.

Key points

Market structure depends on number of firms, product type, entry conditions and knowledge.
Perfect competition: many firms, identical product, free entry, perfect knowledge; firm is a price taker with P = AR = MR.
All firms maximise profit where MC = MR; profit = (AR − ATC) × Q.
Competitive firm’s short-run supply curve is MC above minimum AVC.
Long-run perfect competition: P = MC = minimum AC; normal profit; efficient.
Monopoly: one seller, no close substitutes, barriers; MR < AR; P > MC; supernormal profit can persist.
Price discrimination needs monopoly power, separable markets, no resale and different elasticities; higher price where demand is less elastic.
Monopoly is controlled by competition law, price control, taxation, nationalisation or opening up the market.
Monopolistic competition: differentiated products, free entry; long-run normal profit with excess capacity.
Oligopoly: few interdependent firms; kinked demand explains rigid prices; collusion and cartels such as OPEC.

Start here: What is a market? Classifying market structures

When Nigerians hear "market" they picture Balogun in Lagos, Onitsha Main Market or Kurmi in Kano. To an economist, a market is wider than a place.

A market is any arrangement through which buyers and sellers come into contact to buy and sell a good or service and so determine its price. It may be a physical place, a telephone call, or an online platform.

Markets differ in how much competition there is. Market structure means the features of a market that shape how firms set price and output. Economists classify markets using four main criteria:

Number of sellers (and buyers): very many, many, few or one.
Nature of the product: identical (homogeneous) or differentiated (branded).
Ease of entry and exit: free, or blocked by barriers.
Knowledge: whether buyers and sellers know all prices.

Structure	Sellers	Product	Entry	Control over price
Perfect competition	Very many	Identical	Free	None
Monopolistic competition	Many	Differentiated	Free	Some
Oligopoly	Few	Identical or differentiated	Difficult	Considerable, but interdependent
Monopoly	One	No close substitutes	Blocked	Great

All structures other than perfect competition are called imperfect competition.

Worked example 9.1

Classify each: (a) a hypothetical town where one company holds the only licence to supply piped water; (b) hundreds of hairdressing salons in Enugu, each with its own name and style; (c) three large firms that supply almost all cement in a country (illustrative).

(a) One seller, no close substitute, entry blocked by licence: monopoly.
(b) Many sellers, differentiated service, easy entry: monopolistic competition.
(c) Few dominant sellers: oligopoly.

Monopoly; monopolistic competition; oligopoly

⚠️ Common mistake: defining a market as "a place where goods are bought and sold". Examiners want the wider idea of contact between buyers and sellers, which need not be in one place.

Try it yourself. Name the four criteria for classifying market structures.

Show solution

Number of firms, nature of the product, ease of entry and exit, and knowledge of the market.

Continue this lesson in the free app →

Practice questions

1. Under perfect competition, the individual firm is a

price taker
price maker
monopolist
price leader

Show answer

A: price taker
It cannot influence market price.

2. For a perfectly competitive firm, the demand (AR) curve is

downward sloping
vertical
upward sloping
horizontal at the market price

Show answer

D: horizontal at the market price
P = AR = MR.

3. In the long run under perfect competition, firms earn

losses
monopoly profit
normal profit only
supernormal profit

Show answer

C: normal profit only
Free entry removes supernormal profit.

4. A firm sells 100 units at ₦50 each and its ATC is ₦40. Its supernormal profit is

₦900
₦1,000
₦5,000
₦4,000

Show answer

B: ₦1,000
(AR − ATC) × Q = (50 − 40) × 100.

5. A single seller of a product with no close substitutes is a

monopolist
oligopolist
perfect competitor
duopolist

Show answer

A: monopolist
Monopoly: one seller and barriers to entry.

Key words

Market: Any arrangement through which buyers and sellers come into contact to exchange goods or services.
Market structure: The features of a market, such as number of firms, product type and ease of entry, that shape how firms behave.
Perfect competition: A market with very many buyers and sellers of an identical product, free entry and exit, and perfect knowledge.
Price taker: A firm that must accept the market price because it is too small to influence it.
Price maker: A firm with enough market power to set its own price.
Industry: All the firms producing the same product.
Imperfect competition: Any market that lacks one or more conditions of perfect competition.
Monopoly: A market with a single seller of a product with no close substitutes, protected by barriers to entry.
Barriers to entry: Obstacles that stop new firms from entering an industry, e.g. patents, licences, high capital costs.
Natural monopoly: An industry where one firm can supply the whole market at lower cost than two or more firms.
Price discrimination: Selling the same product at different prices to different buyers for reasons not related to cost.
Monopolistic competition: Many firms selling differentiated products with free entry.

Learn Market structures: perfect competition, monopoly & others step by step, free.
The Cara's Tips app teaches every topic from the very basics, with quick checks, worked examples and exam practice. It works offline.
Open this lesson in the free app Download for Android