Monopoly

IB Economics Higher Level· Microeconomics > Market structure > Monopoly· 25 min read

1. Characteristics and Barriers to Entry★★☆☆☆HL only⏱ 6 min

📘 Definition

Monopoly

A market structure with a single seller of a unique good with no close substitutes, and high barriers to entry that block new firms from entering the market.

Example:

A local water or electricity utility provider in most countries.

Barriers to entry are the key characteristic that allows a monopolist to retain supernormal profit in the long run, unlike perfectly competitive markets.

Legal barriers: Patents, copyrights, government licenses that restrict entry
Natural barriers: Persistent economies of scale leading to natural monopoly
Strategic barriers: Predatory pricing, strong brand loyalty that blocks new entrants
Input control: Ownership or control of a key raw material required for production

📐 Worked Example

A city has total water demand $Q = 1000 - 2 P$ , and any firm supplying water has total cost $T C = 10000 + 50 Q$ . Prove this is a natural monopoly.

1
Calculate average cost (AC) for any firm:
2
$AC = \frac{TC}{Q} = \frac{10000}{Q} + 50$
3
AC falls as output $Q$ increases, meaning economies of scale persist across the entire market demand.
4
If the market is split between two firms each producing 250 units, AC for each firm is:
5
$AC = \frac{10000}{250} + 50 = 90$
6
If a single firm produces 500 units (the full market), AC is:
7
$AC = \frac{10000}{500} + 50 = 70$
8
A single firm supplies the entire market at lower average cost than multiple competing firms, so this is a natural monopoly.

2. Profit Maximizing Equilibrium★★★☆☆HL only⏱ 8 min

📘 Definition

Monopoly Profit Maximization

$Q_{m}$ = monopoly output, $P_{m}$ = monopoly price

The monopolist maximizes profit by producing at the output level where marginal revenue equals marginal cost ( $M R = M C$ ), then sets price from the market demand curve at this output.

Unlike perfect competition, a monopolist faces the entire downward-sloping market demand curve, so marginal revenue lies below the demand curve. For a linear demand curve, the marginal revenue curve is twice as steep as the demand curve.

📐 Worked Example

A monopolist faces demand $P = 100 - Q$ , and total cost $T C = 100 + 10 Q + 0.5 Q^{2}$ . Find the profit-maximizing output, price, and total profit.

1
First derive total revenue and marginal revenue:
2
$TR = P \times Q = (100 - Q)Q = 100Q - Q^2 \\ MR = \frac{dTR}{dQ} = 100 - 2Q$
3
Next derive marginal cost from total cost:
4
$MC = \frac{dTC}{dQ} = 10 + Q$
5
Set $M R = M C$ to find profit-maximizing output:
6
$100 - 2Q = 10 + Q \implies 3Q = 90 \implies Q_m = 30$
7
Find price from the demand curve at $Q_{m} = 30$ :
8
$P_m = 100 - 30 = 70$
9
Calculate total profit as $T R - T C$ :
10
$\pi = (70 \times 30) - (100 + 10(30) + 0.5(30)^2) = 2100 - 850 = \$1250$

3. Welfare Comparison to Perfect Competition★★★☆☆HL only⏱ 7 min

With the same cost structure, monopoly produces a lower output and charges a higher price than perfect competition, leading to net welfare loss for society.

📘 Definition

Deadweight Welfare Loss

The net loss of total consumer plus producer surplus that arises when output is not at the allocatively efficient level (where $P = M C$ ).

📐 Worked Example

Using the same demand and cost functions from the previous example, compare monopoly and perfect competition outcomes and calculate deadweight loss.

1
Allocative efficiency in perfect competition occurs at $P = M C$ :
2
$100 - Q = 10 + Q \implies 2Q = 90 \implies Q_{pc} = 45, \quad P_{pc} = 55$
3
Compare outcomes: Monopoly produces $Q_{m} = 30 < Q_{p c} = 45$ and charges $P_{m} = 70 > P_{p c} = 55$ .
4
Deadweight loss is the area of the welfare triangle:
5
$DWL = 0.5 \times (P_m - MC_{Qm}) \times (Q_{pc} - Q_m) \\ = 0.5 \times (70 - 40) \times (45 - 30) = 225$

Arguments against monopoly: Allocatively inefficient ( $P > M C$ ), productively inefficient (not producing at minimum $A C$ ), increases income inequality by transferring surplus from consumers to the monopolist.
Arguments for some monopolies: Can exploit large economies of scale to produce at lower average cost than many small firms; supernormal profit can fund risky research and development that leads to innovation.

4. Regulation of Monopoly★★★★☆HL only⏱ 6 min

Governments use a range of policies to address the market failure caused by unregulated monopoly. Common policies include price regulation, breaking up monopolies, privatization, public ownership, and trade liberalization.

📐 Worked Example

Evaluate marginal cost pricing regulation for a natural monopoly.

1
Marginal cost pricing sets $P = M C$ , which achieves allocative efficiency and eliminates deadweight loss.
2
For a natural monopoly, average cost is falling across all market output, so $M C < A C$ .
3
At $P = M C$ , price is below average cost, so the firm will make a loss and exit the market unless subsidized by the government.
4
Subsidies require government funding raised from taxation, which creates an opportunity cost and potential deadweight loss from tax itself.
5
A common alternative is average cost pricing, which sets $P = A C$ , allowing the firm to break even, with a smaller deadweight loss than unregulated monopoly.

5. Common Pitfalls

Wrong move:

Drawing the marginal revenue curve above the demand curve.

Why:

Confuses monopoly demand with perfect competition, where marginal revenue equals price.

Correct move:

Marginal revenue always lies below the downward-sloping demand curve for a monopolist; it is twice as steep for linear demand.

Wrong move:

Assuming all monopolies earn supernormal profit in the long run.

Why:

Ignores that profit depends on the position of average cost relative to market demand.

Correct move:

A monopolist with high fixed costs or falling market demand can make losses in the long run.

Wrong move:

Setting price equal to marginal cost at the profit-maximizing equilibrium.

Why:

Confuses the allocative efficiency condition with the monopolist's profit-maximizing rule.

Correct move:

Profit-maximizing output is always at $M R = M C$ , and price is read from the demand curve at that output, so $P > M C$ .

Wrong move:

Claiming all monopolies are always harmful to the economy.

Why:

Ignores potential benefits of natural monopoly economies of scale and innovation funded by supernormal profit.

Correct move:

Evaluation requires considering specific context: natural monopolies are often more efficient than multiple competing small firms.

6. Quick Reference Cheatsheet

Characteristic	Monopoly	Perfect Competition
Number of firms	One	Many
Barriers to entry	Very high	None
Demand curve (firm)	Downward sloping (market demand)	Horizontal (price taker)
Profit max rule	$M R = M C$ , $P > M R = M C$	$M R = M C = P$
Allocative efficiency	No ( $P > M C$ )	Yes ( $P = M C$ )
Productive efficiency	No (not at min AC)	Yes (long run, at min AC)
Long run supernormal profit	Yes	No (zero profit)

7. Frequently Asked

Is a monopolist guaranteed to earn profit?

No. If average cost is higher than the demand curve at all output levels, a monopolist can make losses, especially when facing high fixed costs or falling market demand.

Can a monopolist set any price they want?

No. Monopolists are constrained by the market demand curve: raising price beyond a certain point will cause total revenue to fall as quantity demanded drops too sharply.

When this came up on past exams

AI-estimated based on syllabus patterns — cross-check with official past papers for accuracy. Use only as revision-focus signals.

2025 · Paper 1
10m: Compare monopoly vs perfect competition
2024 · Paper 2
15m: Evaluate monopoly regulation policies
2023 · Paper 1
15m: Analyze natural monopoly characteristics

Going deeper

SyllabusIB Economics HL SyllabusOfficial unit 2 syllabus reference

What's Next

Monopoly is the first of the imperfectly competitive market structures you will study for IB HL Economics, and its core concepts of downward-sloping demand, profit maximization and welfare analysis apply to all other imperfect market structures. Understanding monopoly is also foundational for the extension topic of price discrimination, which is frequently tested in higher-mark Paper 1 questions. Next, you will build on this knowledge to study other common imperfect market structures that exist in most real-world economies.