What you'll learn

• What economists mean by market failure and why it matters.
• How consumer surplus and producer surplus link to efficiency.
• The main sources of market failure: public goods, externalities, monopoly power, information problems, inequality and price volatility.
• How to identify the socially efficient output and the welfare loss on externality diagrams.

1. Efficiency: the benchmark

A free market is a market where prices and quantities are mainly determined by buyers and sellers, rather than direct government control. Economic agents are the decision-makers in an economy: consumers, firms, workers and government.

In a simple competitive market, the demand curve shows the marginal private benefit (MPB): the benefit to consumers from one extra unit. The supply curve shows the marginal private cost (MPC): the cost to firms of producing one extra unit. Marginal just means “one additional”.

The free market equilibrium is where quantity demanded equals quantity supplied. At this point, there is no pressure for price to rise or fall.

Consumer surplus is the extra benefit consumers receive when they pay less than the maximum price they were willing to pay. Producer surplus is the extra benefit producers receive when they sell for more than the minimum price they were willing to accept.

If there are no external costs, no external benefits, good information and strong competition, the free market equilibrium output maximises total surplus: consumer surplus plus producer surplus.

2. What market failure means

Economic welfare means the overall wellbeing or satisfaction gained from the use of scarce resources. In diagrams, we often measure welfare using surplus. A deadweight welfare loss is a loss of total surplus that is not gained by anyone else.

3. Public goods and private goods

A private good is both rival and excludable. Rival means one person’s consumption reduces what is available for others. Excludable means non-payers can be prevented from using it. A sandwich is a private good.

A public good is both non-rival and non-excludable. Non-rival means one person’s use does not reduce availability for others. Non-excludable means it is difficult or impossible to stop non-payers benefiting. Examples include national defence, street lighting and flood defences.

The key market failure is the free-rider problem: people can benefit without paying, so private firms may not be able to earn enough revenue to supply the good. Consumers may want the good, but producers lack a profitable way to charge for it. Government may therefore provide it using taxation.

4. Merit and demerit goods

A merit good is a good or service that tends to be underconsumed in a free market, often because consumers underestimate its long-term private benefits or ignore its wider social benefits. Examples include education, vaccinations and preventative healthcare.

A demerit good is a good or service that tends to be overconsumed in a free market, often because consumers underestimate its long-term private costs or ignore costs imposed on others. Examples include cigarettes, alcohol and some high-sugar products.

For consumers, this may mean choices that damage future health, skills or income. For government, it can raise spending pressures, such as NHS costs. For firms, there may be profits from selling demerit goods even when social welfare falls.

5. Externalities: third-party effects

A marginal external cost (MEC) is the extra cost imposed on third parties from one more unit. A marginal external benefit (MEB) is the extra benefit received by third parties from one more unit.

The social curves include both private and external effects:

$$\begin{array}{rl}MSC& =MPC+MEC\\ MSB& =MPB+MEB\end{array}$$

Marginal social cost (MSC) is the full cost to society of one extra unit. Marginal social benefit (MSB) is the full benefit to society of one extra unit.

Negative production externalities

A negative production externality occurs when production creates external costs. For example, a factory may emit pollution that worsens local air quality. The firm considers its MPC, but society faces MSC, so the free market output is too high.

Negative consumption externalities

A negative consumption externality occurs when consumption creates external costs. For example, smoking in public or excessive alcohol consumption may impose costs on others. Here, MPB is above MSB, so the good is overconsumed.

Positive consumption externalities

A positive consumption externality occurs when consumption creates external benefits. Vaccinations protect the person vaccinated and also reduce transmission to others. MPB is below MSB, so the good is underconsumed.

6. Monopoly power

Monopoly power is the ability of a firm to influence price or output because it faces limited competition. This may come from barriers to entry, which are obstacles preventing new firms entering a market, such as patents, high start-up costs, network effects or control of key resources.

A firm with monopoly power can restrict output and charge a higher price than in a competitive market. Consumers lose because prices are higher and choice may be lower. The firm gains higher profit, but society loses if output falls below the efficient level.

In the diagram below, average revenue (AR) is revenue per unit, which is the demand curve. Marginal revenue (MR) is the extra revenue from selling one more unit. Marginal cost (MC) is the extra cost of producing one more unit.

7. Information asymmetries and gaps

An information gap exists when buyers or sellers lack important information. Information asymmetry exists when one side of the market has more or better information than the other.

Examples include used cars, insurance, private pensions, rental housing and energy tariffs. Consumers may overpay, buy unsuitable products or underestimate risks. Good firms may struggle if consumers cannot distinguish high quality from low quality. Government may respond through regulation, labelling rules or consumer protection.

8. Absence of private property rights

Private property rights are legal rights to own, use, sell or exclude others from a resource. If property rights are missing or weak, resources may be overused because no one has enough incentive to protect them.

This can create the tragedy of the commons, where individuals acting in their own interest overuse a shared resource. Examples include overfishing, deforestation and carbon emissions. Current producers and consumers may gain, but future generations and wider society face costs.

9. Income inequality

Income inequality is an uneven distribution of income between households or groups. Markets allocate goods according to ability and willingness to pay, not according to need.

This may be seen as a market failure because low-income households may underconsume essentials such as nutritious food, heating, housing or education. In the UK cost-of-living squeeze, higher energy and food prices hit lower-income households hardest because necessities take up a larger share of their income.

Inequality can also reduce efficiency in the long run if it limits access to education, training or healthcare, weakening human capital.

10. Volatile prices

Price volatility means large and frequent price changes. It is common in markets where supply or demand is inelastic, such as agricultural products, gas, oil and housing.

For consumers, volatile prices create uncertainty and affordability problems. For producers, unstable revenues make investment and planning harder. For government, sharp price rises can create inflationary pressure and political pressure to intervene, as seen during global energy shocks after Russia’s invasion of Ukraine.