If supply curve is positively sloped i.e , it slopes upwards from left to right then we have to look at its exact position in space(on graph). If it originates from origin then its elasticity will be one. If it originates from any point left to origin on the X-axis (second quadrant) , its elasticity will be greater than one i.e. supply will be elastic. If it originates from any point right to origin on the X-axis (first quadrant), its elasticity will be less than one i.e., supply will be inelastic.
In extreme cases if supply curve runs parallel to X-axis (zero slope), its elasticity will be infinity i.e. it will be perfectly elastic and if it runs parallel to Y-axis (slope infinite), its elasticity will be zero i.e., supply will be perfectly inelastic.
It will be Zero / perfectly inelastic supply. It occurs when quantity supplied remains unchanged with change in price.
Price Elasticity of Supply = 0