Elasticity of Supply (PES) measures responsiveness of quantity supplied to price changes. Formula: PES = % Change in Quantity Supplied / % Change in Price. Typically positive (unlike demand). Elastic supply (>1): Easily expandable production, flexible inputs (manufactured goods). Inelastic supply (<1): Fixed resources, time constraints (agriculture in short run, land). Determinants: Availability of substitute resources (elastic if available), Time period (more elastic in long run), Production flexibility, Storage costs. Agricultural supply: Inelastic in short run (land/season fixed), more elastic long run (adjust acreage). Manufacturing: More elastic (flexible production). Perfectly elastic (horizontal): Zero cost increase (rare). Perfectly inelastic (vertical): Fixed supply regardless of price (land in very short run). Real example: Coffee supply is inelastic because cultivation takes years; wheat supply is more elastic in long run. ICAI questions: Calculation, comparison with demand elasticity, time-period effects. Exam tip: "Agricultural supply is inelastic short-run but elastic long-run" is a frequently tested concept.