Dark Pools Part I: What Is It And How Does It Work?

Is it doing the breast stroke in the dark? If it were only that simple but in today's complex trading world there exists a mysterious and illiquid private market called, Dark Pools. Even though they only account for 12% of activity, when combined with wholesale brokers they suck up almost one-third of U.S. stock trading order flow away from public exchanges. Yet the controversy is that the public doesn't know what's being transacted and how much, hence the name. Even with only about 50 operators, MIT Sloan's Professor Haoxiang Zhu has studied how they're having a significant impact on investors and exchanges. Read on to learn more about what he uncovered on this shadowy market…

Dating back to the era of big hair and high tops of the 1980's, dark pools were established to avoid large block orders from influencing financial markets and ensure privacy. For almost 25 years all was well as pool activity was a mere three to five percent but then in 2007 the SEC passed Regulation NMS (National Market System), which allowed investors to bypass public exchanges to gain price improvements.

Since then broker-dealers began to setup their own pools in concert with algorithmic trading and decimalization and as a result, bid-ask spreads shriveled and trading costs declined with institutional investors and BB following suite. Instead, now a public exchange quote at $10.00-$10.05 can be beaten by the pool at a fractional mid-point spread of say $10.025 bypassing the NMS sub-penny rule…"And trader's like that", says Linette Lopez in her article, What The Heck Is A Dark Pool And Why Are People Trading In Them?

Essentially, there are two types of order routing to dark pools:
1. Indications of Interest – in which pool information only on ticker symbol, price, and buy/sell interest goes to brokers.
2. Payment for Order Flow – where a broker favors a specific pool in sending orders.

However, once the actual order is received it's either an IOC (immediate or cancel) or an FOK (fill or kill), both synonymous with HFT activity on quote stuffing and pinging. To clarify how this works, I've provided a flow chart of a typical order routing decision tree.

Dark Pool Trading

In Professor Zhu's paper, Do Dark Pools Harm Price Discovery he argues that even if an investor gains a price improvement, the delay in execution may be harmful and that it entails greater risk and volatility. First, information traders entail a greater risk as their information becomes stale and a possible herd movement begins due to transaction delays. Second, the longer the delay in execution, the greater the odds that the price could move against them once the herd gains momentum, hence the volatility.

He also finds that these information traders are self-selecting and go back to the exchanges where market-makers price-in these price improvements and as such spreads widen as they protect themselves while uninformed traders, such as hedgers, remain in the pool and subtract liquidity.

Thus, if Zhu is correct then dark pools are widening spreads on public exchanges!

Lastly, keep an eye out for DARK POOLS PART II, where I will discuss their advantages and how the exchanges are trying to compete against them otherwise this topic is wide open, so any comments, concerns, or questions you monkeys have, let 'em rip!

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