How can this be? The answer is that is cannot. Around the world, a number of exchanges and regulators have recognized this fact. We in the US are acknowledging it too. Increasingly vigorous competition between exchanges, ECNs, ATSs and foreign trading markets has shifted significant amounts of market share away from the primary markets. This heightened competition has spurred innovation in trading systems and responsiveness to customers, as well as reduced trading costs. On the other hand, trading in multiple markets has increased concerns about potential gaps in the surveillance of intermarket trading. Plus, loss of market share may translate into fewer revenues supporting an SRO's regulatory functions, without reducing the SRO's oversight responsibilities.