What Is a Dark Pool?

A dark pool is a private financial forum or exchange for trading securities. Dark pools allow investors to trade without exposure until after the trade has been executed. Dark pools are a type of alternative trading system that give investors the opportunity to place orders and make trades without publicly revealing their intentions during the search for a buyer or seller.

Understanding the Dark Pool

Dark pools emerged in the 1980s when the Securities and Exchange Commission (SEC) allowed brokers to transact large blocks of shares. Electronic trading and an SEC ruling in 2007 that was designed to increase competition and cut transaction costs have stimulated an increase in the number of dark pools. Dark pools can charge lower fees than exchanges because they are often housed within a large firm and not necessarily a bank.

For example, Bloomberg LP owns the dark pool Bloomberg Tradebook, which is registered with the SEC. Dark pools were historically mostly used by institutional investors for block trades involving a large number of securities. However, dark pools are no longer used only for large orders. A study by Celent found that the average order size dropped from 430 shares in 2009 to approximately 200 shares in 2013.

The primary advantage of dark pool trading is that institutional investors making large trades can do so without exposure while finding buyers and sellers. This prevents heavy price devaluation, which would otherwise occur. If it were public knowledge, for example, that an investment bank was trying to sell 500,000 shares of a security, the security would almost certainly have decreased in value by the time the bank found buyers for all of their shares. Devaluation has become an increasingly likely risk, and electronic trading platforms are causing prices to respond much more quickly to market pressures. If the new data is reported only after the trade has been executed, however, the news has much less of an impact on the market.

There are several different types of dark pools: broker or dealer-owned exchanges, such as Morgan Stanley's MS Pool and Goldman Sachs' Sigma X; independently owned exchanges offering private trading to their clients; and private exchange markets operated by public exchanges such as the New York Stock Exchange's Euronext. A privately-owned market will have price discovery within their own markets, but a dark pool operated by a broker derives its prices from public exchanges.

Because of their sinister name and lack of transparency, dark pools are often considered by the public to be dubious enterprises. In reality, dark pools are tightly regulated by the SEC. However, there is a real concern that because of the sheer volume of trades conducted on dark markets, the public values of certain securities are increasingly unreliable or inaccurate. There is also mounting concern that dark pool exchanges provide excellent fodder for predatory high-frequency trading (HFT).