Equilibrium Price and Quantity
Equilibrium Price Definition in Economics
Graphical Method
Table Method
Price ($) | Quantity Demanded | Quantity Supplied |
10 | 100 | 50 |
12 | 90 | 70 |
14 | 80 | 80 |
16 | 70 | 90 |
Algebraic Method
Surplus and Shortage Dynamics
Market Disequilibrium: Price Ceilings and Shortages
Equilibrium Type | Scope | Key Feature | Typical Context |
Economic Equilibrium | General | Balance of aggregate market forces | Macro & micro markets |
Competitive Equilibrium | Market | Efficient allocation under perfect competition | Perfectly competitive markets |
Perfect Competition Equilibrium | Market | Price‑taking behavior by all agents | Theoretical benchmark markets |
General Equilibrium | Economy‑wide | Simultaneous balance across multiple markets | Interconnected markets |
Underemployment Equilibrium | Economy | Equilibrium with excess labor | Keynesian macro context |
Lindahl Equilibrium | Specific | Voluntary contribution to public goods | Public goods provision |
Intertemporal Equilibrium | Temporal | Balance across time periods | Savings & investment decisions |
Nash Equilibrium | Strategic | No incentive to unilaterally deviate | Strategic/oligopolistic environments |
Economic Equilibrium
Competitive Equilibrium
Perfect Competition and Competitive Equilibrium
Condition | Theory | Reality |
# of sellers | Very large | Often limited |
Product differentiation | None | Common |
Entry/exit | Free | Restricted by regulation |
Information | Perfect | Imperfect |
General Equilibrium
Underemployment Equilibrium
Lindahl Equilibrium
Intertemporal Equilibrium
Nash Equilibrium
Market Structure | # of Firms | Product Type | Price Control | Equilibrium Price | Efficiency | Examples |
Perfect Competition | Many | Homogeneous | None (Price-taker) | P = MC | Max. allocative & productive | Wheat, foreign exchange |
Monopoly | One | Unique (no substitutes) | Full (Price-maker) | P > MC | Inefficient (deadweight loss) | Local water utility, patented drug |
Oligopoly | Few | Either | Shared (strategic) | P between monopoly & PC | Varies; depends on cooperation | Airlines, smartphone makers |
Monopolistic Competition | Many | Differentiated | Some | P > MC (but lower than monopoly) | Excess capacity, some inefficiency | Coffee shops, clothing brands |
Perfect Competition: The Efficiency Benchmark
Monopoly Equilibrium
Oligopoly Equilibrium
Monopolistic Competition
Factor | Shift Direction | Price Effect | Quantity Effect |
Increase in consumer demand | Demand ↑ | Price ↑ | Quantity ↑ |
Technological improvement | Supply ↑ | Price ↓ | Quantity ↑ |
Rise in input costs | Supply ↓ | Price ↑ | Quantity ↓ |
Population growth | Demand ↑ | Price ↑ | Quantity ↑ |
Natural disaster (e.g. drought) | Supply ↓ | Price ↑ | Quantity ↓ |
Price Signals and Market Coordination
Elasticity and Adjustment Speed
Short-Run vs Long-Run Adjustment
Impediments to Adjustment
Real-World Adjustment Examples
Condition | At Equilibrium | In Disequilibrium |
Price Behavior | Stable | Tends to rise or fall |
Quantity Supplied | Equals quantity demanded | Not equal to demand |
Market Outcome | All goods sold | Unsold goods or unmet demand |
Incentives | Balanced for buyers/sellers | Encourage changes in behavior |
Consumer and Producer Surplus
Allocative Efficiency
Productive Efficiency
Limitations of the Efficiency Concept
Criterion | At Equilibrium (Perfect Competition) | Under Price Control (e.g., Ceiling) |
Consumer Surplus | Maximized | May increase for some |
Producer Surplus | Maximized | Decreases |
Total Welfare | Maximized | Decreases (Deadweight Loss) |
Resource Allocation | Efficient (P = MC) | Distorted |
Price Signal Accuracy | High | Low |
Qd = Qs
1. Use the Supply Function for Quantity
2. Use the Demand Function for Quantity
3. Set the Two Quantities Equal in Terms of Price
4. Solve for the Equilibrium Price
Strategic Pricing and Nash Equilibrium
Firm A ↓ \ Firm B → | Low Price | High Price |
Low Price | (3,3) | (5,1) |
High Price | (1,5) | (4,4) |
What is meant by equilibrium price?
How do you explain equilibrium price simply?
How do you find equilibrium price on a graph?
Is equilibrium price a good thing?
What causes market equilibrium?
What is an example of a market equilibrium?
What happens when price is above equilibrium?
What happens when price is below equilibrium?
Can there be multiple equilibrium prices?
How quickly do markets reach equilibrium?