A price ceiling is a government- or group-imposed price control, or limit, on how high a price is charged for a product, commodity, or service. Governments use price ceilings ostensibly to protect consumers from conditions that could make commodities prohibitively expensive. Such conditions can occur during periods of high inflation, in the event of an investment bubble, or in the event of monopoly ownership of a product, all of which can cause problems if imposed for a long period without controlled rationing, leading to shortages. Further problems can occur if a government sets unrealistic price ceilings, causing business failures, stock crashes, or even economic crises. In unregulated market economies, price ceilings do not exist.