What is the Law of One Price? The Law of One Price is a law that provides for equity securities to be priced according to how much they are worth in the market. The Law of One Price states that all equal securities, fungible with one another, must have the same value and therefore be represented by the same price in the market. The Law of One Price means that all stocks must have the same price for the market to function properly. The Law of One Price is the basis for the stock market to be centralized and standardized, all under the same price for each type of security