Vertical supply curve (perfectly inelastic supply)

When demand D₁ is in effect, the price will be P₁. When D₂ is occurring, the price will be P₂. The equilibrium quantity is always Q, and any shifts in demand will only affect price.

If the quantity supplied is fixed in the very short run no matter what the price, the supply curve is a vertical line, and supply is called perfectly inelastic.