If market power causes higher prices, lower output and waste, the obvious question is what a government can actually do about it. There are five main tools, and the interesting part of this topic is not listing them — it is explaining why each one only half works.
📘 What you need to know
Governments intervene because the abuse of market power is a source of market failure.
Legislation means writing the laws; regulation means enforcing them, usually through a competition authority.
Regulators block mergers that would create too much market power, and ban price fixing.
Natural monopolies are usually controlled with a maximum price rather than broken up.
Setting price at MC gives allocative efficiency but forces a loss, so a subsidy is needed. Setting price at AC avoids the loss but is not fully efficient.
Other tools: fines, nationalisation, and laws protecting suppliers and employees.
Every tool risks government failure — the cure can cost more than the disease.
Tool 1: competition law and a regulator
The cheapest way to control monopoly power is to stop it forming. Most countries have a competition authority that watches mergers and takeovers, and can block any deal that would leave one firm with too large a share — often around 25% is the trigger for investigation.
The same body outlaws anti-competitive practices: price fixing, output quotas, agreements to keep new firms out, and predatory pricing.
The catch. Investigations take years, big firms can afford better lawyers than the regulator, and tacit collusion leaves no paper trail to find in the first place.
Tool 2: price regulation
Where competition is impossible — a water network, a rail track — the government leaves the monopoly in place and caps its price instead. But at what level? There are two candidates, and they pull in opposite directions.
Both caps make consumers better off than P1. The choice between them is really a choice about who pays: at P2 the customers cover the full cost, at P3 the taxpayer covers part of it.
🤔 Why marginal cost pricing creates a loss
A natural monopoly has enormous fixed costs, so its ATC curve is still falling even at the market’s full demand. If ATC is falling, MC must lie below ATC. Set price equal to MC and price is therefore below average cost at every output — the firm cannot cover its fixed costs. The efficiency is real, but somebody has to pay for it.
Tools 3, 4 and 5
Approach
How it works
The problem with it
Fines
Regulators fine firms a percentage of sales revenue for anti-competitive behaviour
Cases drag on for years, firms settle for less, and the fine is often smaller than the profit made from breaking the rules
Nationalisation
The state takes ownership, so the aim becomes service rather than profit
State firms can be run inefficiently, the money has an opportunity cost, and government may lack the expertise
Protecting suppliers
Anti-monopsony laws and minimum prices stop a dominant buyer squeezing its suppliers
Hard to police contract terms and payment delays across thousands of suppliers
Protecting workers
Minimum wage, working-hours limits, and the right to join a trade union
Firms may respond by cutting hours or jobs; enforcement is patchy in some sectors
The fines row is the one to remember for evaluation. A fine only changes behaviour if it is bigger than the profit from the bad behaviour. If it is smaller, a rational firm simply treats it as a cost of doing business.
Evaluating intervention
Arguments for stepping in
Lower prices and more output for consumers
Corrects allocative and productive inefficiency
Protects small suppliers and workers from a dominant firm
Keeps essential services affordable
Arguments for caution
Over-regulation can deter investment and innovation
Regulators may lack the information firms have
Capping profit too tightly removes the money for research
How much profit is “fair” is a normative judgement, not a fact
🧩 How to structure a 15-mark evaluation on this
Define market power and say why it is market failure.
Diagram: monopoly or regulated natural monopoly, fully labelled.
Analyse one policy in depth — the chain from policy to price to consumer.
Evaluate: short run against long run, consumers against firms, and the risk of government failure.
Conclude with a judgement that depends on something: the industry, the size of the fine, the quality of the regulator.
Worked examples
WORKED EXAMPLE 1
A regulator can fine firms 10% of sales revenue. A firm with sales of $600m made an extra $90m of profit by fixing prices. Calculate the fine and comment on whether it will change behaviour. [3]
Step 1: Calculate the fine10% of $600m = 0.10 × 600Fine = $60mStep 2: Compare with the gainProfit from price fixing = $90m, fine = $60mStep 3: Judgement
The firm still keeps $30m, so the fine does not remove the incentive.
Too small to deter: the firm gains even after payingDeterrence is about the size of the fine relative to the gain, not the size of the number.
WORKED EXAMPLE 2
A regulator caps a water company’s price at marginal cost, $6 per unit. Output is then 16 million units and ATC is $9.75. (a) Calculate the firm’s loss. (b) Explain the policy problem this creates. [4]
(a) Loss = (ATC – price) × Q= (9.75 – 6.00) × 16m = 3.75 × 16mLoss = $60 million(b) Why it happens
ATC is still falling, so MC lies below ATC and a price equal to MC cannot cover average cost.
The policy problem
The firm will not supply at a loss, so the government must pay a subsidy of $60m.
Allocative efficiency is achieved, but taxpayers fund itThat opportunity cost is the evaluation point: the $60m could have gone to schools or hospitals.
💡 Exam tip
Name a specific tool rather than writing “the government should intervene”. Marks follow named policies.
Always draw the natural monopoly diagram with MC below ATC. If MC cuts ATC on your sketch, the whole answer breaks.
Link every policy to price and output. That is the mechanism examiners want to see.
Use “government failure” as a technical term, not just as criticism.
Say clearly who gains and who loses. Consumers, firms, workers, suppliers and taxpayers all sit differently.
Finish with a conditional judgement: “this works provided that the regulator has good cost information”.
⚠ Common mix-up
Confusing legislation with regulation. One writes the law, the other enforces it.
Saying regulators break up natural monopolies. They usually cap the price instead, because splitting them raises costs.
Thinking a price cap always helps. Set below average cost, it drives the firm out unless it is subsidised.
Treating a big fine as automatically effective. Compare it with the profit from the behaviour first.
Assuming nationalisation removes inefficiency. It removes the profit motive, which can make efficiency worse.
Forgetting monopsony. Market power over suppliers matters as much as power over consumers.
Up next: Why Free Markets Produce Unequal Outcomes — moving from how markets set prices to whether the results are fair.
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