Difficulty: Intermediate | Prerequisites: Basic supply and demand (Chapter 4), equilibrium price and quantity.
Governments regularly intervene in markets by setting legal limits on prices. This chapter sits at the heart of any introductory or intermediate micro course because it bridges the pure supply-and-demand model you already know with the messy reality of policy. You should be comfortable drawing supply and demand curves, finding equilibrium, and understanding what surplus and shortage mean before diving in. The payoff is a framework you will use again in welfare economics, labour economics, and public finance.
A price floor sets a legal minimum (e.g. minimum wage); a price ceiling sets a legal maximum (e.g. rent control). Either one only changes outcomes when it forces the price away from equilibrium, in which case it creates a surplus or a shortage. Price controls often hurt the very people they are designed to help, particularly in the long run when supply and demand become more elastic.
Price control
A government-imposed legal limit on the price of a good or service. Think of it as the government stepping in and saying "the price is not allowed to go above (or below) this number."
Price floor
A legal minimum price below which a good or service may not be sold. In simple terms, the government says "you cannot charge less than this amount." The classic example is the minimum wage.
Price ceiling
A legal maximum price above which a good or service may not be sold. In simple terms, the government says "you cannot charge more than this amount." Rent control is the textbook example.
Binding constraint
A price control that forces the market price away from its equilibrium level. A price floor is binding when it is set above equilibrium; a price ceiling is binding when it is set below equilibrium. Think of it as: the control only "bites" when it prevents the market from reaching the price it would naturally settle on.
Non-binding constraint
A price control set at a level that does not interfere with equilibrium. The market clears on its own, and the control has no practical effect.
Surplus (excess supply)
The quantity supplied exceeds the quantity demanded at the prevailing price. In the labour market, a surplus of workers is called unemployment.
Shortage (excess demand)
The quantity demanded exceeds the quantity supplied at the prevailing price. Shortages lead to rationing, whether through queuing, seller discrimination, or other non-price mechanisms.
Rationing mechanisms
The ways a limited supply gets allocated among buyers when the price mechanism is not allowed to do the job. Examples include long queues (first come, first served) and discrimination based on sellers' biases.
Tags: price floor, minimum wage, binding floor, non-binding floor, labour surplus, unemployment
A price floor is a legal minimum price.
If the floor is set below the equilibrium price, it is non-binding and has no effect on the market. The market simply clears at equilibrium as usual.
If the floor is set above the equilibrium price, it is binding. The market price is forced above the level where quantity supplied equals quantity demanded, creating a surplus.
In the labour market, the price floor takes the form of a minimum wage.
The "price" is the hourly wage; the "quantity" is the number of workers.
When the minimum wage sits above the equilibrium wage, more people want to work at that wage than firms want to hire, producing a surplus of labour. That surplus is unemployment.
The labour-market diagram shows supply of labour (S, upward-sloping) and demand for labour (D, downward-sloping) crossing at equilibrium (e.g. $6.00 per hour, 500 workers). A minimum wage above $6.00 raises the wage but reduces the quantity of workers hired below 500.
Price floors can hurt the people they intend to help. Some workers earn a higher wage, but others lose their jobs entirely because firms reduce hiring at the higher mandated wage.
Tags: price ceiling, rent control, binding ceiling, shortage, rationing, non-price allocation
A price ceiling is a legal maximum price.
If the ceiling is set above the equilibrium price, it is non-binding and the market is unaffected. (Ice-cream example: equilibrium at $3, ceiling at $4, no effect.)
If the ceiling is set below the equilibrium price, it is binding. The market price cannot rise to clear the market, so quantity demanded exceeds quantity supplied, creating a shortage. (Ice-cream example: equilibrium at $3, ceiling at $2, shortage of 50 cones since 125 are demanded but only 75 are supplied.)
When a binding ceiling creates a shortage, the price mechanism can no longer allocate the good. The limited supply must be rationed by other means.
Long queues (first come, first served): buyers pay in time rather than money.
Seller discrimination: sellers allocate the scarce good according to their own preferences or biases, which may be arbitrary or unfair.
These non-price rationing mechanisms are generally less efficient and less equitable than the price system, which is one of the central arguments against price ceilings.
Tags: rent control, housing shortage, inelastic supply, elastic supply, landlord incentives, long-run effects
Rent control is the most-examined price ceiling in this course. A local government caps rents with the goal of making housing affordable for lower-income residents. The effects differ sharply depending on the time horizon.
Short run: small shortage
Both supply and demand for housing are relatively inelastic in the short run. Landlords cannot quickly demolish buildings, and tenants cannot quickly relocate.
Because the curves are steep, the gap between quantity demanded and quantity supplied at the controlled rent is small.
The shortage exists but is modest.
Long run: large shortage
Over time, both supply and demand become more elastic.
On the supply side, landlords have little incentive to build new apartments or maintain existing ones when rents are capped. Housing stock shrinks and quality deteriorates.
On the demand side, people are more mobile in the long run. The artificially low rent draws more people into the city, increasing quantity demanded.
The combination of falling supply and rising demand produces a large housing shortage.
The critique is that rent control is a highly inefficient way to improve living standards for the poor. It benefits those who already hold rent-controlled leases while making it harder for newcomers to find housing at all.
Tags: OPEC, 1973 oil crisis, gasoline shortage, gas lines, supply shift, binding ceiling
This case study shows how a non-binding ceiling can become binding when market conditions change.
Before 1973, the U.S. had regulations capping the price of gasoline. Because the equilibrium price sat below the ceiling, the control had no effect on the market.
In 1973, OPEC raised the price of crude oil. This increased the cost of producing gasoline, shifting the supply curve to the left (from S₁ to S₂).
In an unregulated market, the price would have risen from P₁ to P₂, and the quantity would have fallen, but there would have been no shortage.
With the price ceiling in place, the price could not rise above the cap. The ceiling became binding, and a shortage appeared: at the capped price, consumers wanted to buy Q_D but producers were only willing to sell Q_S. The difference (Q_D minus Q_S) was the gasoline shortage.
The visible result was long queues at petrol stations. Both OPEC (supply reduction) and U.S. government regulations (price ceiling preventing adjustment) were responsible.
The gasoline price regulations were eventually repealed, removing the ceiling and allowing the market to clear.
Price floor diagram (labour market): Upward-sloping supply of labour (S) and downward-sloping demand for labour (D). Equilibrium at the intersection (e.g. $6.00, 500 workers). A horizontal line above equilibrium marks the minimum wage. At that wage, read quantity supplied (right along S) and quantity demanded (left along D); the gap is the surplus (unemployment).
Price ceiling diagram (ice-cream market): Standard S and D. A horizontal line below equilibrium marks the ceiling. At that price, quantity demanded exceeds quantity supplied; the gap is the shortage.
Rent control, short run vs long run: Two side-by-side panels. Panel (a) has steep (inelastic) S and D curves and a small shortage at the controlled rent. Panel (b) has flat (elastic) S and D curves and a much larger shortage at the same controlled rent.
Gasoline price ceiling: Two panels. Panel (a) shows the ceiling above equilibrium (non-binding, no effect). Panel (b) shows the supply curve shifted left after the oil price rise, pushing the new equilibrium above the ceiling. The ceiling is now binding, and the gap between Q_D and Q_S is the shortage.
No formulas are required for this topic. The analysis is entirely graphical, using shifts of S and D and the position of the control relative to equilibrium.
Minimum wage laws exist in most developed economies. Debates over raising the minimum wage are debates about where the floor sits relative to equilibrium in different labour markets (a floor that binds in a low-cost rural area may be non-binding in a high-wage city).
Rent control policies in cities like New York and San Francisco illustrate the long-run deterioration of housing stock and persistent shortages predicted by the model.
The 1973 U.S. gasoline crisis is a textbook example of a non-binding ceiling becoming binding after a supply shock, and it is the reason many economists are sceptical of energy price controls during supply disruptions.
Students often think a price floor always creates a surplus. It does not. A floor set below equilibrium is non-binding and has no effect at all.
Students often confuse which control goes which way. Remember: a floor is below your feet (a minimum), a ceiling is above your head (a maximum).
Students sometimes assume rent control helps all renters. In the long run it tends to help current tenants at the expense of future ones, and it reduces both the quantity and quality of housing available.
Students sometimes think the 1973 gas lines were caused entirely by OPEC. The supply reduction by OPEC was necessary, but the shortage and queues were caused by the U.S. price ceiling preventing the market from adjusting.
⚠️ Expect a question asking you to identify whether a given price control is binding or non-binding, and to state the resulting surplus or shortage.
⚠️ Be prepared to draw and label the short-run vs long-run rent control diagrams and explain why the shortage is larger in the long run (more elastic curves).
⚠️ The 1973 gasoline case is a common exam scenario: you may be asked to explain what happens when a supply shock makes a previously non-binding ceiling become binding.
⚠️ "Price controls often hurt those they intend to help" is a conclusion the course wants you to be able to argue with specific examples (rent control reducing housing quality and availability; minimum wage causing unemployment among low-skilled workers).
True or false: A price floor set below the equilibrium price causes a surplus. (False, it is non-binding and has no effect.)
Fill in the blank: A binding price ceiling creates a ______ because quantity demanded exceeds quantity supplied. (shortage)
True or false: Rent control causes a larger housing shortage in the long run than in the short run. (True, because supply and demand are more elastic over longer time horizons.)
Fill in the blank: In the labour market, a surplus of workers caused by a binding minimum wage is called ______. (unemployment)
True or false: The 1973 U.S. gasoline shortage was caused solely by OPEC raising oil prices. (False, the U.S. price ceiling on gasoline also played a key role by preventing prices from adjusting.)
Q: Suppose the equilibrium rent in a city is $1,200 per month and the government imposes a rent ceiling of $900. Is the ceiling binding? What happens to the quantity of apartments supplied and demanded?
A: The ceiling is binding because it is set below the equilibrium price. At $900, quantity demanded rises (more people want apartments at the lower price) and quantity supplied falls (landlords withdraw units or reduce maintenance). The result is a shortage of apartments.
Q: Explain why a minimum wage set at $5.00 per hour has no effect if the equilibrium wage in the market is $8.00 per hour.
A: The minimum wage is a price floor. At $5.00 it sits below the equilibrium wage of $8.00, so it is non-binding. The market is already paying above the floor, and neither employers nor workers are constrained by it.
Q: Using the 1973 gasoline example, explain the difference between a non-binding and a binding price ceiling.
A: Before 1973, the equilibrium price of gasoline was below the price ceiling, so the ceiling was non-binding and had no effect. After OPEC raised crude oil prices, the supply curve shifted left and the new equilibrium price rose above the ceiling. The ceiling became binding, preventing the price from rising to the new equilibrium. The result was a shortage of gasoline and long queues at petrol stations.
Q: Why does rent control produce a larger shortage in the long run than in the short run?
A: In the short run, both supply and demand for housing are inelastic (steep curves), so the gap between quantity demanded and quantity supplied at the controlled rent is small. In the long run, both curves become more elastic: landlords reduce the housing stock (less building, less maintenance) and more people try to move into the city for cheap rent. The larger responses on both sides widen the shortage.
This material connects directly to elasticity (Chapter 5): the size of a surplus or shortage under a price control depends on how elastic supply and demand are, which is exactly why rent control produces a larger shortage in the long run. It also connects to welfare economics and deadweight loss (Chapter 7 and beyond), where you will learn to measure the efficiency cost of price controls using consumer and producer surplus. The tax incidence material in the second half of this lecture (covered in separate notes) builds on the same supply-and-demand framework and uses elasticity to determine who bears the burden.
Price controls, price floor, price ceiling, minimum wage, rent control, binding constraint, non-binding constraint, surplus, shortage, excess supply, excess demand, rationing, queuing, labour market, housing market, gasoline shortage, OPEC oil crisis, 1973 oil embargo, government intervention, market distortion, deadweight loss (preview), supply and demand policy, wage floor, rent cap, controlled price, market equilibrium disruption