The number of firms is only one feature of a market.
A market structure describes characteristics that shape competitive pressure: the number and relative size of firms, how similar their products are and barriers to entry. Perfect competition is a model with many small price-taking sellers of a homogeneous product and free entry; monopolistic competition has many sellers of differentiated products with relatively low entry barriers. Oligopoly has a few significant firms whose choices can affect one another. Monopoly has a single seller in a defined market with strong entry barriers. Real markets do not always fit a model neatly. Define the market before counting firms, and do not infer every outcome from a label.
- Number and size
- Define the market: which products and locations do buyers treat as alternatives? Then identify its main sellers and their relative sizes.
- Product
- Homogeneous products are treated as the same by buyers. Differentiated products have real or perceived differences, such as service, location or brand.
- Entry
- Barriers to entry are obstacles that make it difficult for a new firm to compete. Free entry means no significant entry barriers, not that starting a business costs nothing.
Read the market-structure models
Price taking and market power
A price taker accepts the market price rather than being able to change it. Market power means some ability to influence price or other terms without losing all buyers; it does not require a monopoly.
Interdependence
In oligopoly, one significant firm's choice affects the others. A price cut may attract their customers, so they may respond with their own cuts. The first firm must consider that response; identical conduct is not guaranteed.
| Model | Sellers/products | Entry and competitive feature |
|---|---|---|
| Perfect competition | Many small sellers; homogeneous product | Free entry; price-taking model |
| Monopolistic competition | Many sellers; differentiated products | Relatively low entry barriers; some own-price discretion |
| Oligopoly | A few significant sellers; homogeneous or differentiated | Substantial barriers often present; interdependence |
| Monopoly | Single seller in a defined market | Strong barriers; alternatives still depend on market definition |
Worked example: Cafes and mobile-network providers
A town has many cafes offering different menus and locations, with relatively easy entry. A different market has three large mobile-network providers, costly infrastructure and licensing requirements. No exact market shares are given.
- The cafe description resembles monopolistic competition: many sellers, differentiated offerings and low entry barriers.
- The mobile-network description resembles oligopoly: a few significant firms and substantial entry constraints.
- A cafe may have some discretion over its own price without being a monopoly. Differentiation can create limited market power.
- These classifications alone do not establish profit, efficiency or the exact price. Buyer alternatives, potential entry and firm conduct also matter.
Watch out for this
Any firm that chooses a price is a monopoly.
Many differentiated sellers have some pricing discretion. Monopoly depends on the defined market and lack of other sellers, not simply a price-setting action.
Check your understanding
Many small sellers offer differentiated products and entry is relatively easy. Which model best matches these stated features?
- Monopolistic competition.
- Monopoly.
- Perfect competition.