---
title: "Perfectly Inelastic Supply | Macro Economics"
description: "Perfectly inelastic supply means quantity supplied stays fixed no matter the price, shown by a vertical supply curve in Principles of Macroeconomics."
canonical: "https://fiveable.me/principles-macroeconomics/key-terms/perfectly-inelastic-supply"
type: "key-term"
subject: "Principles of Macroeconomics"
unit: "Unit 5"
---

# Perfectly Inelastic Supply | Macro Economics

## Definition

Perfectly inelastic supply is a supply situation where quantity supplied does not change when price changes. In Principles of Macroeconomics, it is shown with a vertical supply curve.

## What It Is

Perfectly inelastic supply is a situation in Principles of Macroeconomics where sellers supply the same quantity no matter what happens to price. If price rises, quantity supplied stays the same. If price falls, quantity supplied still stays the same. On a graph, that shows up as a vertical supply curve.

That vertical shape means the price elasticity of supply is zero. In other words, the seller has no ability or no incentive to change output in response to price. This is the extreme end of inelastic supply, so it is not the normal case for most everyday goods. Most markets have at least some ability to increase or decrease output over time.

You usually see perfectly inelastic supply when the quantity is fixed by nature, by time, or by rules. A classic example is a ticket for a concert that is already sold out. Once the event starts, there are only so many seats, and no price change can create more. A similar macro example is land in a specific location, or a highly limited resource that cannot be produced quickly.

In macro, this idea matters because it changes how you think about price adjustment. If demand rises in a market with perfectly inelastic supply, the main thing that changes is price, not quantity. That is why vertical supply can lead to sharp price increases after a demand shock.

This also helps you separate supply response from production ability. A firm or market may want to sell more, but if there is no extra capacity, no available inputs, or a rule caps output, supply stays fixed. The key idea is not that sellers are refusing to respond. It is that they cannot increase quantity supplied at all at that moment.

## Why It Matters

Perfectly inelastic supply shows how a market reacts when quantity cannot adjust. That makes it a good tool for reading supply and demand graphs in Principles of Macroeconomics, especially when a shock changes price but leaves output unchanged.

It also connects directly to elasticity, which is one of the core skills in this unit. If you know supply is perfectly inelastic, you know price elasticity of supply equals zero, so any demand shift will mostly show up as a price change. That is a useful shortcut when you are interpreting graph questions or comparing different market structures.

The concept also gives you a clean way to think about scarce resources and capacity limits. Some goods cannot be produced more quickly, even if prices rise. When that happens, the market clears through higher prices instead of higher quantity.

In class, this term often shows up when you explain why a market reacts strongly to demand changes, why some prices spike after a shock, or why quantity stays fixed in the short run. It is one of the clearest examples of how scarcity and constraints shape market outcomes.

## Connections

### Price Elasticity of Supply

Perfectly inelastic supply is the zero point on the price elasticity of supply scale. If a supply curve is vertical, the quantity supplied never changes, so elasticity is zero. This makes it a useful benchmark when you compare more flexible markets to fixed-capacity markets.

### [Inelastic Supply](/principles-macroeconomics/key-terms/inelastic-supply)

Inelastic supply means quantity supplied changes a little when price changes, but not very much. Perfectly inelastic supply is the extreme version of that idea, where quantity supplied does not change at all. Many real markets are inelastic in the short run, but not perfectly inelastic.

### Supply Curve

The supply curve is the graph you use to show how quantity supplied responds to price. For perfectly inelastic supply, the curve is vertical instead of upward sloping. That visual tells you immediately that price changes affect the market price, not the amount produced.

### [Perfectly Elastic Supply](/principles-macroeconomics/key-terms/perfectly-elastic-supply)

This is the opposite extreme. With perfectly elastic supply, quantity supplied changes at a fixed price, so the supply curve is horizontal. Comparing the two helps you see how elasticity changes whether price or quantity does most of the adjusting.

## On the AP Exam

A quiz or problem set may give you a graph and ask you to identify a vertical supply curve or predict what happens when demand shifts. Your job is to say that quantity supplied stays fixed while price changes. If the scenario describes a fixed number of seats, a limited natural resource, or a short-run capacity limit, that is a strong clue that supply is perfectly inelastic.

You may also be asked to compare it with elastic or inelastic supply using price elasticity of supply. A full-credit answer usually names the fixed quantity, explains why sellers cannot expand output, and then traces the effect on equilibrium price and quantity.

## Perfectly Inelastic Supply vs Perfectly Elastic Supply

These are opposites. Perfectly inelastic supply means quantity supplied never changes, no matter the price, so the curve is vertical. Perfectly elastic supply means sellers will supply any quantity at one specific price, so the curve is horizontal. If you mix them up on a graph, you usually reverse which variable is fixed.

## Key Takeaways

- Perfectly inelastic supply means quantity supplied stays fixed even when price changes.
- The graph is a vertical supply curve, and the price elasticity of supply is zero.
- This shows up when output is capped by capacity, time, rules, or a truly limited resource.
- When demand changes in a perfectly inelastic market, price does the adjusting, not quantity.
- It is an extreme case, so many real markets are only inelastic, not perfectly inelastic.

## FAQs

### What is perfectly inelastic supply in Principles of Macroeconomics?

It is a supply situation where the quantity supplied does not change at all when price changes. On a graph, the supply curve is vertical. In macro, this usually describes a market with a fixed amount of output, like a limited number of seats or a resource that cannot be expanded quickly.

### How do you graph perfectly inelastic supply?

You draw a vertical line at the fixed quantity supplied. The line shows that no matter how high or low the price moves, quantity stays the same. That is why the curve is not upward sloping like a normal supply curve.

### What is the difference between inelastic supply and perfectly inelastic supply?

Inelastic supply means quantity supplied changes only a little when price changes. Perfectly inelastic supply is stricter, because quantity supplied does not change at all. So perfectly inelastic supply is the extreme case of inelastic supply.

### Why does demand shift affect price more than quantity with perfectly inelastic supply?

Because the quantity cannot change, the market cannot respond by producing more or less. A rise in demand pushes up price instead. That is a common graph question in macro, especially when the supply side is fixed in the short run.

## Related Study Guides

- [5.3 Elasticity and Pricing](/principles-macroeconomics/unit-5/3-elasticity-pricing/study-guide/EGzdnMCS0vp8C915)
- [5.1 Price Elasticity of Demand and Price Elasticity of Supply](/principles-macroeconomics/unit-5/1-price-elasticity-demand-price-elasticity-supply/study-guide/rrnH4IGsxQaS78mi)

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