How Do World Prices Determine Imports and Exports?
Autarky means no international trade. Put price per unit vertically and quantity per period horizontally. Domestic demand D slopes down and supply S slopes up. Their intersection E is the no-trade equilibrium. Pw denotes the world price, which a small price-taking country cannot materially change.
Builds on: How Does Trade Create Gains and Adjustment Costs?
What you will learn
- Below the no-trade price, imports fill excess domestic demand; above it, exports absorb excess domestic supply.
- Explain consumer and producer surplus changes
- State the assumptions behind gains from trade
Essential definitions
- Consumer surplus
- Willingness to pay above the amount consumers actually pay.
- Producer surplus
- Revenue above producers’ variable opportunity costs, represented above supply and below price in the model.
- Small price-taking country
- An economy whose trade does not materially change the world price in the market considered.
Read the market before opening trade
Autarky means no international trade. Put price per unit vertically and quantity per period horizontally. Domestic demand D slopes down and supply S slopes up. Their intersection E is the no-trade equilibrium. Pw denotes the world price, which a small price-taking country cannot materially change.
At a given price, move horizontally to each curve and down to read quantity demanded, Qd, and quantity supplied, Qs. If Pw is below the autarky price, buyers want more than domestic firms supply. Imports = Qd − Qs. Domestic production falls and consumption rises as the price moves to Pw under free trade.
Explain gains without confusing transfers and welfare
Consumer surplus is buyers' willingness to pay above what they pay: below demand and above price. Producer surplus is receipts above variable opportunity costs: above supply and below price. Lower import prices increase consumer surplus but reduce domestic producer surplus.
With competition and no externalities or adjustment costs, the consumer gain exceeds the producer loss. That net gain is distinct from the redistribution between them. If Pw is above the autarky price, supply exceeds domestic demand and exports = Qs − Qd. Producers gain more than domestic consumers lose, but domestic food buyers may still face hardship.
HL: turn quantities into payments
Use the same currency and period for all values. Import expenditure = Pw × imports; export revenue = Pw × exports. With Pw of 20 dollars per unit, Qd of 80 and Qs of 40 thousand units per month, imports are 40 thousand and expenditure is 800 thousand dollars per month.
At price 40, Qs of 80 and Qd of 40 thousand give exports of 40 thousand and export receipts of 1,600 thousand dollars. These are payments, not surplus. Assess employment transitions, market power and environmental costs separately when applying the simple model.
Calculate imports at the world price
- In the diagram, Pw = 20 dollars per unit; Qs = 40 and Qd = 80 thousand units per month.
- Imports = Qd − Qs = 80 − 40 = 40 thousand units per month.
- Import expenditure = price × imports = 20 × 40 = 800 thousand dollars per month.
The trade gap is a quantity; multiplying it by price gives a money flow.
Free trade: an importing market
Below the autarky price, domestic demand exceeds supply. Imports fill the gap. Consumers gain and domestic producers lose; the shaded triangle is the net gain under the model assumptions.
How to read this diagram
- Put price per unit vertically and quantity per month horizontally. Draw domestic D and S meeting at the no-trade equilibrium E.
- Add a horizontal world-price line below that equilibrium.
- Project Qs and Qd to the quantity axis; imports are Qd − Qs.
Green: net gain from trade. E is the no-trade intersection of domestic D and S. D: Qd = 120 − 2P. S: Qs = 2P. Values are illustrative; calculations are HL.
- Consumer price / producer receipts
- 20 / 20 dollars per unit
- Domestic output / consumption
- 40 / 80 thousand units
- Imports
- 40 thousand units
On a small screen, scroll the graph horizontally to read all labels.
Assumptions and limits: Small competitive economy, no transport costs or externalities, unlimited imports at the world price. Numerical welfare calculations are HL.
Free trade: an exporting market
Above the autarky price, supply exceeds domestic demand. Exports fill the gap. Producers gain and domestic consumers lose; the shaded triangle shows the net gain.
How to read this diagram
- Put price vertically and quantity per month horizontally. Draw domestic D and S meeting at E.
- Place world price above the autarky equilibrium.
- Mark Qd and Qs; exports are Qs − Qd.
Green: net gain from trade. E is the no-trade intersection of domestic D and S. D: Qd = 120 − 2P. S: Qs = 2P. Values are illustrative; calculations are HL.
- Consumer price / producer receipts
- 40 / 40 dollars per unit
- Domestic output / consumption
- 80 / 40 thousand units
- Exports
- 40 thousand units
On a small screen, scroll the graph horizontally to read all labels.
Assumptions and limits: Small competitive exporter; domestic and international buyers face the same price. Numerical calculations are HL.
Apply and evaluate
- Aggregate surplus gains rely on competitive pricing and the absence of unpriced externalities.
- Compensation and transition support affect whether people harmed by trade share in national gains.
Common misconceptions
- An export opportunity can raise prices for domestic consumers.
- Transfers between producers and consumers are not automatically deadweight losses.
Knowledge check
Who loses directly when an exporting good’s domestic price rises to the world price?
What to remember
Below the no-trade price, imports fill excess domestic demand; above it, exports absorb excess domestic supply. Total gains in the simple model can coexist with losses for particular groups.
Completion records your reflection, not a test score.
Lessons in this section
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