Alternative Trading Systems: Description of ATS Trading in National Market System Stocks

This paper discusses descriptive statistics on U.S. equity Alternative Trading Systems (ATSs, some of which are referred to as “dark pools”). The paper is intended to inform public discussion of the role and regulation of ATSs. While ATSs operate markets similar in some ways to the registered exchanges, there are important institutional differences. Although both exchanges and ATSs provide marketplaces for buyers and sellers to transact in securities, ATSs do not necessarily provide public information on the best prices available to traders within their system. They also do not set rules governing the conduct of subscribers and they perform no self-regulation, while exchanges perform all of these functions. Additionally, because ATSs are regulated as broker-dealers, they comply with a different set of regulations than traditional exchanges. Trading on ATSs regularly comprises 10-15% of U.S. equity trading volume. However, academic and public understanding of ATSs lags that of traditional exchanges partially due to a lack of publicly available data on ATSs. Using a five-day sample of regulatory data from May 7-11, 2012, this paper discusses summary statistics on ATS participation in the trading of National Market System (NMS) stocks, including common stocks and many exchange-traded products (ETPs).