<P> In economics, a shortage or excess demand is a situation in which the demand for a product or service exceeds its supply in a market . It is the opposite of an excess supply (surplus). </P> <P> In a perfect market (one that matches a simple microeconomic model), an excess of demand will prompt sellers to increase prices until demand at that price matches the available supply, establishing market equilibrium . In economic terminology, a shortage occurs when for some reason (such as government intervention, or decisions by sellers not to raise prices) the price does not rise to reach equilibrium . In this circumstance, buyers want to purchase more at the market price than the quantity of the good or service that is available, and some non-price mechanism (such as "first come, first served" or a lottery) determines which buyers are served . So in a perfect market the only thing that can cause a shortage is price . </P>

When do a shortage or surplus of products occur
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