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Supply and demand

The price P of a product is determined by a balance between production at each price (supply S) and the desires of those with purchasing power at each price (demand D). The diagram shows a positive shift in demand from D1 to D2, resulting in an increase in price (P) and quantity sold (Q) of the product.

Supply and demand is an economic model of price determination in a market. It concludes that in a competitive market, the unit price for a particular good will vary until it settles at a point where the quantity demanded by consumers (at current price) will equal the quantity supplied by producers (at current price), resulting in an equilibrium of price and quantity.
The four basic laws of supply and demand are:[1] 1. If demand increases and supply remains unchanged, then it leads to higher equilibrium price and quantity. 2. If demand decreases and supply remains unchanged, then it leads to lower equilibrium price and quantity. 3. If supply increases and demand remains unchanged, then it leads to lower equilibrium price and higher quantity. 4. If supply decreases and demand remains unchanged, then it leads to higher price and lower quantity.

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The graphical representation of supply and demand
The supply-demand model is a partial equilibrium model representing the determination of the price of a particular good and the quantity of that good which is traded. Although it is normal to regard the quantity demanded and the quantity supplied as functions of the price of the good, the standard graphical representation, usually attributed to Alfred Marshall, has price on the vertical axis and quantity on the horizontal axis, the opposite of the standard convention for the representation of a mathematical function.
Determinants of