Classify supply as elastic, inelastic, unit elastic, perfectly elastic or perfectly inelastic
Explain the determinants of PES including the role of time
Apply PES to real markets including housing and factor markets
Price Elasticity of Supply
What is PES?
Key Formula
PES = % change in Quantity Supplied ÷ % change in Price
PES measures how responsive producers are to a price change. Unlike PED, PES is always positive (law of supply: higher price → more supplied). The value tells us how flexible production is.
PES > 1 → ELASTIC
Producers respond strongly to price changes — easy to scale up output quickly.
PES < 1 → INELASTIC
Producers struggle to respond — output is constrained by time, capacity, or resources.
Price Elasticity of Supply
PES Values at a Glance
0
Perfectly Inelastic
Supply fixed regardless of price. Land, original art, Stradivarius violins
0–1
Inelastic
Supply rises, but less than proportionately. Housing, skilled labour, oil
1
Unit Elastic
Supply rises proportionately with price. All curves through the origin are unit elastic.
>1
Elastic
Supply rises more than proportionately. Mass-produced goods, standardised commodities
∞
Perfectly Elastic
Any price change leads to infinite supply response. Purely theoretical.
Price Elasticity of Supply
Supply Curves: Elastic vs Inelastic
S₁ = Elastic supply (shallow slope)
S₂ = Inelastic supply (steep slope)
P = Price · Q = Quantity
ELASTIC SUPPLY (shallow)
A small price rise → large increase in quantity supplied. Producers have spare capacity, flexibility, and can react quickly.
INELASTIC SUPPLY (steep)
A large price rise → small increase in quantity supplied. Constrained by long production times, scarce inputs, or fixed capacity.
EXAM NOTE
A supply curve through the origin is always unit elastic (PES=1), regardless of slope. Curves intercepting the price axis = elastic; quantity axis = inelastic.
Determinants of PES
What Determines PES?
Spare capacity: Firms with unused machinery/workers can increase output quickly → higher PES.
Stock levels: Large inventories allow firms to supply more immediately without increasing production → higher PES in short run.
Time period: PES is almost always more elastic in the long run as firms can build new capacity, hire, and enter the market.
Factor mobility: If land, labour, and capital can easily switch to producing the good, PES is higher.
Production period: Goods requiring long production (aircraft, oak trees, whisky) have very low PES — you can't speed up time.
Perishability: Perishable goods must be sold quickly — supply cannot be stored or delayed, limiting flexibility.
Time & PES
The Short Run vs Long Run
MOMENTARY (Immediate)
Supply is perfectly inelastic. Whatever is already produced is all that's available. Think: fish caught today, today's newspaper print run.
SHORT RUN
Some factors are fixed (factory size). Firms can use more labour or raw materials, but can't build new factories. Supply is relatively inelastic.
LONG RUN
All factors are variable. Firms can build new factories, new firms enter, workers retrain. Supply becomes much more elastic.
AGRICULTURAL EXAMPLE
If wheat prices surge, farmers cannot instantly plant more — the crops are already in the ground. PES in the immediate term = ~0. In the following season, farmers plant more wheat. After 2–3 seasons, new farms specialise in wheat. PES gradually rises toward elastic.
Real-World Application · UK Housing
The UK Housing Crisis: Inelastic Supply in Action
🏠 THE NUMBERS
UK house prices rose +65% from 2010–2022. Over the same period, new housing completions barely changed — averaging ~170,000 homes/year against a target of 300,000. PES for UK housing ≈ 0.2–0.4 — extremely inelastic.
🔒 WHY IS SUPPLY SO INELASTIC?
Planning system: Getting planning permission takes years.
Land scarcity: Green Belt restrictions limit buildable land.
Construction time: A house takes 12–18 months to build after approval.
NIMBY opposition: Local resistance slows permissions.
💡 THE KEY INSIGHT
When supply is inelastic, demand increases translate almost entirely into higher prices, not higher output. This is why Help-to-Buy subsidies (boosting demand) worsened affordability — they pushed prices up without fixing the supply constraint. The solution must be on the supply side: reform planning, release Green Belt land, build social housing. This is a live political debate in UK economics.
Real-World Application · Labour Markets
Perfectly Inelastic Supply: Scarce Talent
🎬
A-List Hollywood Talent
Supply of a specific individual is perfectly inelastic in the short run — there is only one of any given person.
THE ECONOMICS OF STAR POWER
Studios compete intensely for A-list actors (Scarlett Johansson, Dwayne Johnson, etc.) because they can't substitute one for another — audiences pay specifically for them. This drives salaries to extraordinary levels: Scarlett Johansson reportedly earned $55m in a single year (2019). PES ≈ 0 in the short run.
LONG-RUN SUPPLY RESPONSE
Over time, new stars emerge (supply becomes more elastic) — but this takes years of talent development. The same logic applies to Premier League footballers, top surgeons, or specialist engineers. In each case, the inelastic short-run supply is why wages are so high.
🎓 EXAM LINK
This example links PES to the labour market (Theme 1.4). When PES of labour is very low, wages are high and competition for talent is fierce. When PES of labour is high (unskilled work), wages stay low.
Policy Applications
Why PES Matters for Policy
TAX INCIDENCE
When PES is low (inelastic supply), producers absorb more of a tax — they can't easily cut output. When PES is high, producers pass more of the tax onto consumers via higher prices.
SUBSIDY EFFECTIVENESS
Subsidies to inelastic industries (e.g. farming) mainly raise producer profit rather than increasing output much. Subsidies to elastic industries translate into larger output gains — better value for government money.
PRICE VOLATILITY
When both supply AND demand are inelastic, small shocks produce large price swings. This explains why oil, housing, and agricultural markets are notoriously volatile.
LONG-RUN POLICY
Governments can improve PES through investment in skills (more elastic labour supply), infrastructure, and reducing planning barriers. Supply-side policies aim to make the economy's supply more responsive.
Evaluation
Evaluating PES
Strengths
Explains price volatility in key markets (oil, housing, food)
Guides tax and subsidy policy — who really bears the burden?
Helps firms plan production capacity and inventory
Links neatly to the SR/LR distinction throughout microeconomics
Limitations
PES is difficult to estimate precisely — data on production responses is limited
PES varies widely within sectors (luxury vs standard housing)
Technology changes can rapidly shift PES — historical estimates may not apply
Assumes rational profit-maximising producers — not always realistic
Essay Tip: When discussing supply-side shocks or tax incidence, always state the PES of the relevant market explicitly. A strong evaluation point: PES improvements take time — governments cannot make supply elastic overnight, which limits short-run policy options.
Glossary
Key Terms
PES
Price elasticity of supply. % change in Qs ÷ % change in P. Always positive.
Elastic Supply
PES > 1. Quantity supplied responds more than proportionately to a price change.
Inelastic Supply
PES < 1. Supply responds less than proportionately. Common in SR and resource-constrained markets.
Spare Capacity
Unused production capacity. Higher spare capacity → higher PES, as output can increase without new investment.
Short Run
Period in which at least one factor of production is fixed. Supply tends to be more inelastic.
Tax Incidence
The division of a tax burden between producers and consumers, determined by relative elasticities of supply and demand.
Question 1 of 8 · Price Elasticity of Supply
House prices rise 40% over 5 years, but new housing completions rise only 8%. What does this suggest about the PES of housing?
A
PES = 5 — supply is highly elastic
B
PES = 0.2 — supply is highly inelastic
C
PES = 1 — supply is unit elastic
D
PES = −0.2 — supply is negatively elastic
Answer · Question 1
House prices rise 40% over 5 years, but new housing completions rise only 8%. What does this suggest about the PES of housing?
A
PES = 5 — supply is highly elastic
B
PES = 0.2 — supply is highly inelastic
C
PES = 1 — supply is unit elastic
D
PES = −0.2 — supply is negatively elastic
Correct: B. PES = % change in Qs ÷ % change in P = 8% ÷ 40% = 0.2. This is highly inelastic (0 < PES < 1). PES is always positive (law of supply), so D is impossible. This exactly mirrors the UK housing crisis — large price rises producing tiny supply responses.
Question 2 of 8 · Price Elasticity of Supply
Which factor would most increase the PES of a manufactured good?
A
A long production period
B
High perishability of the product
C
Significant spare production capacity
D
Highly specialised, immobile factors of production
Answer · Question 2
Which factor would most increase the PES of a manufactured good?
A
A long production period
B
High perishability of the product
C
Significant spare production capacity
D
Highly specialised, immobile factors of production
Correct: C. Spare capacity means firms can increase output immediately without new investment, making supply highly responsive to price — high PES. Long production periods and immobile factors reduce PES. Perishability limits a firm's ability to store and time supply, but doesn't directly increase PES.
Question 3 of 8 · Price Elasticity of Supply
In the immediate run (momentary period), supply is best described as:
A
Perfectly elastic — producers can supply any amount
B
Unit elastic — supply changes proportionately with price
C
Perfectly inelastic — supply is fixed at whatever has already been produced
D
Highly elastic — firms can redirect resources instantly
Answer · Question 3
In the immediate run (momentary period), supply is best described as:
A
Perfectly elastic — producers can supply any amount
B
Unit elastic — supply changes proportionately with price
C
Perfectly inelastic — supply is fixed at whatever has already been produced
D
Highly elastic — firms can redirect resources instantly
Correct: C. In the momentary period, whatever is produced is the total supply available — it cannot be increased. A fisherman who has caught 200 fish that morning cannot catch more just because prices rise that afternoon. PES = 0 momentarily. Over longer time periods, PES increases as producers can adjust.
Question 4 of 8 · Price Elasticity of Supply
The UK government subsidises new house construction but prices barely fall. This is most likely because:
A
Demand for housing is perfectly elastic
B
The supply of housing is highly elastic, so prices fall quickly
C
The PES of housing is very low, so the subsidy mainly raises builder profit rather than output
D
The subsidy reduces demand rather than increasing supply
Answer · Question 4
The UK government subsidises new house construction but prices barely fall. This is most likely because:
A
Demand for housing is perfectly elastic
B
The supply of housing is highly elastic, so prices fall quickly
C
The PES of housing is very low, so the subsidy mainly raises builder profit rather than output
D
The subsidy reduces demand rather than increasing supply
Correct: C. With very inelastic supply (PES ≈ 0.2), a subsidy shifts S slightly right but output barely increases — most benefit accrues to producers as higher margins. The underlying planning and land constraints prevent a large supply response. This is why economists argue that fixing housing requires structural supply-side reform, not just subsidies.
Question 5 of 8 · Price Elasticity of Supply
Which supply curve has PES = 1 (unit elastic) regardless of its slope?
A
A supply curve that is perfectly vertical
B
Any supply curve that passes through the origin
C
A supply curve that is perfectly horizontal
D
A supply curve that intercepts the quantity axis
Answer · Question 5
Which supply curve has PES = 1 (unit elastic) regardless of its slope?
A
A supply curve that is perfectly vertical
B
Any supply curve that passes through the origin
C
A supply curve that is perfectly horizontal
D
A supply curve that intercepts the quantity axis
Correct: B. A mathematically provable result: any straight-line supply curve through the origin has PES = 1 at every point, regardless of steepness. A vertical supply curve = PES 0 (perfectly inelastic). A horizontal supply curve = PES = ∞ (perfectly elastic). Curves intercepting the price axis have PES > 1; quantity axis have PES < 1.
Question 6 of 8 · Price Elasticity of Supply
Over time, the PES of most goods tends to:
A
Decrease as markets become more competitive
B
Stay constant — PES is a fixed property of the good
C
Increase — producers can adjust capacity and new firms can enter in the long run
D
Become negative as supply becomes harder to maintain
Answer · Question 6
Over time, the PES of most goods tends to:
A
Decrease as markets become more competitive
B
Stay constant — PES is a fixed property of the good
C
Increase — producers can adjust capacity and new firms can enter in the long run
D
Become negative as supply becomes harder to maintain
Correct: C. Time is the single most important determinant of PES. In the long run, all factors become variable — firms can build new factories, workers can retrain, and new firms can enter. Wheat farmers who can't adjust this season can switch crops next season. PES is always higher in the long run than the short run.
Question 7 of 8 · Price Elasticity of Supply
A tax is imposed on a good with perfectly inelastic supply (PES = 0). Who bears the entire tax burden?
A
Consumers — they pay higher prices
B
Producers — they cannot reduce output to avoid the tax
C
The burden is split equally between consumers and producers
D
The government — tax revenue falls to zero
Answer · Question 7
A tax is imposed on a good with perfectly inelastic supply (PES = 0). Who bears the entire tax burden?
A
Consumers — they pay higher prices
B
Producers — they cannot reduce output to avoid the tax
C
The burden is split equally between consumers and producers
D
The government — tax revenue falls to zero
Correct: B. With perfectly inelastic supply, producers cannot reduce output — they must sell exactly the same quantity regardless of price. The tax therefore falls entirely on producers, squeezing their margin. This is why land value taxes are popular with economists: land supply is fixed (PES=0), so the tax falls entirely on landowners without distorting economic activity.
Question 8 of 8 · Price Elasticity of Supply
Whisky takes at least 3 years to mature. Which statement about the supply of aged Scotch whisky is most accurate?
A
Supply is perfectly elastic — distilleries can produce as much as needed
B
Supply is highly inelastic in the short run due to the fixed maturation period
C
Supply is unit elastic because whisky prices and output move proportionately
D
PES is negative because higher prices discourage production
Answer · Question 8
Whisky takes at least 3 years to mature. Which statement about the supply of aged Scotch whisky is most accurate?
A
Supply is perfectly elastic — distilleries can produce as much as needed
B
Supply is highly inelastic in the short run due to the fixed maturation period
C
Supply is unit elastic because whisky prices and output move proportionately
D
PES is negative because higher prices discourage production
Correct: B. The minimum maturation period makes it physically impossible to respond to a price surge with more supply in the short run — whatever was put in casks 3 years ago is what's available today. In the long run, distilleries can increase production now to sell in 3+ years' time, making PES more elastic. This is also why rare aged whiskies (12, 18, 25 year) command enormous price premiums — supply is even more constrained.