Market structures and barriers to entry
Market structures and barriers to entry: build the core model, apply it to evidence and qualify conclusions where outcomes depend on context.
9708 section 7.6; A Level. Checked against Cambridge's 2026–2028 Version 2 (latest version published December 2025) and 2029 Version 1 (published September 2026). Cambridge states that neither version has significant changes affecting teaching. Always follow the syllabus for the candidate's examination year.
Before you begin
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which combination best describes monopolistic competition?
What you will learn
- Compare perfect competition, monopoly, monopolistic competition, oligopoly and natural monopoly
- Classify structures by sellers, product differentiation, entry and information
- Explain legal, market, cost and physical barriers to entry and exit
Core model and terms
Market structure depends on the number and size of buyers and sellers, product differentiation, freedom of entry and information. Perfect competition is a benchmark with many small firms and homogeneous products; monopoly has one dominant seller; monopolistic competition combines many firms with differentiated products; oligopoly has a few interdependent firms. Natural monopoly can arise where one supplier serves the market at lower average cost than multiple providers.
Apply and evaluate
Barriers can be legal, market-based, cost-related or physical. Patents may be legal; brand loyalty or network effects may be market barriers; large sunk costs may deter entry; geography or infrastructure can create physical limits. Classify using evidence and distinguish a legal monopoly from a firm that merely has a high market share.
Pause and explain
Which statement best applies market structures and barriers to entry?
Worked example
A city’s water network has very high fixed infrastructure cost and lower average cost when one network serves the whole market. Which structure may fit, and why?
Show the worked solution
- One network can spread fixed cost over more users
- Competing networks may duplicate expensive pipes
- The market may have natural-monopoly characteristics
Answer One network can spread fixed cost over more users → Competing networks may duplicate expensive pipes → The market may have natural-monopoly characteristics
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
A city’s water network has very high fixed infrastructure cost and lower average cost when one network serves the whole market. Which structure may fit, and why?
Give me a hint
Consider whether duplicating fixed infrastructure raises unit cost.
Compare my reasoning
- One network can spread fixed cost over more users
- Competing networks may duplicate expensive pipes
- The market may have natural-monopoly characteristics
One network can spread fixed cost over more users Competing networks may duplicate expensive pipes The market may have natural-monopoly characteristics
Look for these in your work
- One network can spread fixed cost over more users
- Competing networks may duplicate expensive pipes
- The market may have natural-monopoly characteristics
A firm has a patent for a new medicine. Identify the entry barrier and state one condition that shapes its effect.
Give me a hint
Focus on the legal right that restricts copying.
Compare my reasoning
- The patent grants temporary legal protection
- It can prevent direct imitation
- Its effect depends on duration, substitutes, regulation and potential entry after expiry
The patent grants temporary legal protection It can prevent direct imitation Its effect depends on duration, substitutes, regulation and potential entry after expiry
Look for these in your work
- The patent grants temporary legal protection
- It can prevent direct imitation
- Its effect depends on duration, substitutes, regulation and potential entry after expiry
Three firms dominate a market but sell differentiated brands and face few new entrants. Which features point to oligopoly?
Give me a hint
Use seller concentration and strategic interdependence.
Compare my reasoning
- A small number of firms hold most sales
- Each firm’s choices can affect rivals
- The market has oligopolistic features, though other evidence also matters
A small number of firms hold most sales Each firm’s choices can affect rivals The market has oligopolistic features, though other evidence also matters
Look for these in your work
- A small number of firms hold most sales
- Each firm’s choices can affect rivals
- The market has oligopolistic features, though other evidence also matters
A firm has a high market share but faces close substitutes and easy entry. Why is share alone insufficient to prove monopoly power?
Give me a hint
Consider constraints on pricing and future entry.
Compare my reasoning
- Substitutes limit buyers’ alternatives less
- Entry can attract new competitors
- Market share alone does not establish durable power over price
Substitutes limit buyers’ alternatives less Entry can attract new competitors Market share alone does not establish durable power over price
Look for these in your work
- Substitutes limit buyers’ alternatives less
- Entry can attract new competitors
- Market share alone does not establish durable power over price
Common mistakes
- Classifying a market from firm count alone or treating a high market share as proof of an unconstrained monopoly.
What can you explain now?
Which combination best describes monopolistic competition?
Compare with the explanation
Many firms, differentiated products and relatively open entry
Differentiation gives some market power while entry can constrain long-run returns.
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Make it stick
Before moving on, explain the central idea in market structures and barriers to entry and state one condition that could change its effect.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.