Perfectly Elastic Supply

Supply is said to be perfectly or infinitely elastic if the price is fixed at all levels of demand.  The demand curve has been shown in the above diagram for the sake of clarity.

If the supply is perfectly elastic, the supply curve is a horizontal straight line and the elasticity of supply is equal to infinity.

When demand increases from quantity supplied increases but price stays fixed .  Conversely, if demand falls, quantity supplied falls  but price stays fixed.

This is the case of Government price control.