# Monopoly

> IB Economics Higher Level · Microeconomics Unit 2
> Source: https://www.owlsprep.com/study/ib-economics-hl-u2-monopoly/

This subtopic covers monopoly characteristics, barriers to entry, diagrammatic equilibrium analysis, welfare comparisons to perfect competition, and regulatory policy responses, a core heavily tested HL microeconomics topic.

**Prerequisites:** [Perfect competition](https://www.owlsprep.com/study/ib-economics-hl-u2-perfect-competition/); [Cost and revenue curves](https://www.owlsprep.com/study/ib-economics-hl-u2-cost-revenue-curves/); [Welfare and surplus analysis](https://www.owlsprep.com/study/ib-economics-hl-u2-welfare-analysis/)

## Learning objectives

- Define monopoly and identify types of barriers to entry
- Draw and interpret monopoly profit-maximizing equilibrium diagrams
- Compare monopoly welfare outcomes to perfect competition
- Evaluate common government policies to regulate monopoly

## Characteristics and Barriers to Entry

**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 $Q = 1000 - 2P$, and any firm supplying water has total cost $TC = 10000 + 50Q$. 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.

## Profit Maximizing Equilibrium

**Monopoly Profit Maximization** — The monopolist maximizes profit by producing at the output level where marginal revenue equals marginal cost ($MR=MC$), then sets price from the market demand curve at this output.

*Notation:* $Q_m$ = monopoly output, $P_m$ = monopoly price

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.

> **tip**
>
> Always label the profit max output where $MR=MC$, then trace up to the demand curve to get price. This is the most commonly mis-marked step in monopoly diagram questions.

**Worked example:** A monopolist faces demand $P = 100 - Q$, and total cost $TC = 100 + 10Q + 0.5Q^2$. 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 $MR = MC$ 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 $TR - TC$:
10. $$\pi = (70 \times 30) - (100 + 10(30) + 0.5(30)^2) = 2100 - 850 = \$1250$$

## Welfare Comparison to Perfect Competition

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.

**Deadweight Welfare Loss** — The net loss of total consumer plus producer surplus that arises when output is not at the allocatively efficient level (where $P=MC$).

**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 $P=MC$:
2. $$100 - Q = 10 + Q \implies 2Q = 90 \implies Q_{pc} = 45, \quad P_{pc} = 55$$
3. Compare outcomes: Monopoly produces $Q_m=30 < Q_{pc}=45$ and charges $P_m=70 > P_{pc}=55$.
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 ($P>MC$), productively inefficient (not producing at minimum $AC$), 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.

## Regulation of Monopoly

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 $P=MC$, which achieves allocative efficiency and eliminates deadweight loss.
2. For a natural monopoly, average cost is falling across all market output, so $MC < AC$.
3. At $P=MC$, 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 $P=AC$, allowing the firm to break even, with a smaller deadweight loss than unregulated monopoly.

**Exam command terms**

Common command terms for monopoly questions in IB exams have specific expectations:

- **Evaluate** — You must discuss both advantages and disadvantages of the policy/outcome, and end with a supported conclusion. *(Evaluate the use of price capping for private natural monopolies.)*

- **Compare and contrast** — Explicitly state similarities and differences, and use diagrammatic evidence to support your answer. *(Compare and contrast welfare outcomes of monopoly and perfect competition.)*

## Common pitfalls

- **Wrong:** Drawing the marginal revenue curve above the demand curve.
  - Why it fails: Confuses monopoly demand with perfect competition, where marginal revenue equals price.
  - Correct: Marginal revenue always lies below the downward-sloping demand curve for a monopolist; it is twice as steep for linear demand.
- **Wrong:** Assuming all monopolies earn supernormal profit in the long run.
  - Why it fails: Ignores that profit depends on the position of average cost relative to market demand.
  - Correct: A monopolist with high fixed costs or falling market demand can make losses in the long run.
- **Wrong:** Setting price equal to marginal cost at the profit-maximizing equilibrium.
  - Why it fails: Confuses the allocative efficiency condition with the monopolist's profit-maximizing rule.
  - Correct: Profit-maximizing output is always at $MR=MC$, and price is read from the demand curve at that output, so $P>MC$.
- **Wrong:** Claiming all monopolies are always harmful to the economy.
  - Why it fails: Ignores potential benefits of natural monopoly economies of scale and innovation funded by supernormal profit.
  - Correct: Evaluation requires considering specific context: natural monopolies are often more efficient than multiple competing small firms.

## 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 | $MR=MC$, $P>MR=MC$ | $MR=MC=P$ |
| Allocative efficiency | No ($P>MC$) | Yes ($P=MC$) |
| Productive efficiency | No (not at min AC) | Yes (long run, at min AC) |
| Long run supernormal profit | Yes | No (zero profit) |

## 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.

- [Monopolistic competition and oligopoly](https://www.owlsprep.com/study/ib-economics-hl-u2-monopolistic-competition-and-oligopoly/)
- [Game theory for oligopoly (HL only)](https://www.owlsprep.com/study/ib-economics-hl-u2-game-theory-for-oligopoly/)

---

From [OwlsPrep](https://www.owlsprep.com) — free study guides for A-Level, IB, AP and IGCSE, written against the official syllabus. Canonical page: https://www.owlsprep.com/study/ib-economics-hl-u2-monopoly/