In a standard supply-and-demand graph, what term describes a supply curve that is vertical at every price?

A vertical supply curve represents perfectly inelastic supply, meaning the quantity supplied remains unchanged when price changes.

On a graph, quantity is usually placed on the horizontal axis and price on the vertical axis. A vertical curve fixes the quantity at one level, so buyers may offer more or less, but producers do not change the amount available in response to price. The price can move along the curve while quantity stays constant.

This model is useful for goods or resources whose supply cannot quickly expand. A fixed quantity of land is a standard example, and a unique collectible may also have a fixed short-run supply. In practice, most supplies are not perfectly inelastic forever; the condition usually describes a particular time period or an idealized case.

Perfectly inelastic supply differs from perfectly elastic supply. Perfectly elastic supply is shown by a horizontal curve: suppliers will provide any amount at one price, while a vertical curve keeps quantity fixed despite price changes.