The issuer itself has the right incentives to choose between trading in one place and trading in many, because its investors will capture the gains or feel the losses. But under current law in the United States, the issuer has no say in the matter-a new market can trade the firm's stock, or options on its stock, or other derivatives based on its stock, without the issuer's consent. A study by Yakov Amihud and Haim Mendelson shows that when a firm's securities (or options on its securities) begin to trade on an additional market, the bid-asked spread rises about half of the time and falls the other half