This article includes a list of references, but its sources remain unclear because it has insufficient inline citations. In modern economies, prices are generally expressed in units of some form of currency. For commodities, they are expressed as currency per investimento bitcoin exchange weight of the commodity, e.

In many financial transactions, it is customary to quote prices in other ways. The most obvious example is in pricing a loan, when the cost will be expressed as the percentage rate of interest. The total amount of interest payable depends upon credit risk, the loan amount and the period of the loan. Other examples can be found in pricing financial derivatives and other financial assets. This requested amount is often called the asking price or selling price, while the actual payment may be called the transaction price or traded price.

Economic price theory asserts that in a free market economy the market price reflects interaction between supply and demand: the price is set so as to equate the quantity being supplied and that being demanded. When a commodity is for sale at multiple locations, the law of one price is generally believed to hold. This essentially states that the cost difference between the locations cannot be greater than that representing shipping, taxes, other distribution costs and more. The paradox of value was observed and debated by classical economists.