Wall Street's Secretive and Dangerous Dark Pools
Some markets allow dark liquidity to be posted inside the existing limit order book alongside public liquidity, usually through the use of iceberg orders. Iceberg orders generally specify an additional display quantity, smaller than the overall order quantity. The order is queued along with other orders but only the display quantity is printed to the market depth. When the order reaches the front of its price queue, only the display quantity is filled before the order is automatically put at the back of the queue and must wait for its next chance to get a fill. Such orders will therefore get filled less quickly than the fully public equivalent, and they often carry an explicit cost penalty in the form of a larger execution cost charged by the market. Iceberg orders are not truly dark either, as the trade is usually visible after the fact in the
market's public trade feed.
Truly dark liquidity can be collected off-market in dark pools. Dark pools are generally very similar to standard markets with similar order types, pricing rules and prioritization rules. However the liquidity is deliberately not advertised - there is no market depth feed. Such markets have no need of an iceberg order type. In addition they prefer not to print the trades to any public data feed, or if legally required to do so, will do so with as large a delay as legally possible - all to reduce the market impact of any trade. Dark pools are often formed from brokers' order books and other off-market liquidity. When comparing pools careful checks should be made as to how liquidity numbers were calculated - some venues count both sides of the trade, or even count liquidity that was posted but not filled.
Whilst it is safe to say that trading on a dark venue will reduce market impact it must be noted that it is very unlikely to reduce it to zero. In particular the liquidity that crosses with you has to come from somewhere - and at least some of it is likely to come from the public market, as automated broker systems intercept market-bound orders and instead cross them with you. This disappearance of the opposite side liquidity as it trades with you and leaves the market will cause impact. In addition your order will slow down the market movement in the direction favourable to you and speed it up in the direction unfavourable to you. The market impact of your hidden liquidity is greatest when all of the public liquidity has a chance to cross
with you and least when you are only able to cross with other hidden liquidity that isn't also represented on the market. In other words you still have a trade-off: reduce your speed of execution by only crossing with dark liquidity or increase it and increase your market impact
Imputing the Existence of Dark Liquidity
There are a few ways to guess at the existence of dark liquidity. If you are watching the market depth and see that both the bid and offer have decreased by the same amount, you might reasonably assume that the trade was in fact made, but at a venue not visible to you. However this is unreliable, since there is the chance that two orders were simply canceled at the same time.
If you are actively trading at a dark venue and choose to take liquidity at a given price then you obviously have a piece of information known only to one other participant (the counterparty in the trade!). Additionally if you were completely filled you may reasonably assume that some more liquidity exists at the same price.
Dark pools are open to gaming, but it is a risky business, predicated on being able to guess both the existence of large liquidity and the pricing mechanism being used. As an example suppose that, by whatever means, you believe that there is a large amount of hidden liquidity, say a buyer pegged to the public bid price. If the public market has much less quantity than you suspect is hidden on the bid, you can buy a similar amount of the asset, pushing up the price. Once the price is high enough, you place a limit price buy order of sufficient quantity onto the public market and
simultaneously place a limit price sell order for the total quantity you just bought on the dark venue. You now hope that the hidden order will cross with you at the current high price bringing the profit. This is a dangerous game though: how do you know that the pegged order is really in the dark pool, and how do you know what the volume is? Finally there is also the chance that another market participant will see the anomalous move, decide the market is mispriced, and take it back to the original price without you being able to liquidate your position at a favourable price.
Unlike many other dark pools operating in the United States, MS POOL does not solicit order flow from external parties by leaking information regarding current client order flow. MS POOL also prevents the potential for gaming and manipulative trading behavior by not accepting immediate or cancel (IOC) orders.
Highlighting the inherent flaws in the entire dark pool product is quite a novel way to differentiate yourself from the competition. Also, as the Wikipedia disclosure points out, substantial dark pool usage is a terrific way for parties who may have "semi-legal" information about a company (and have access to a dark pool) to transact in its stock without alerting regulators or the general public, as dumping 100 million shares ahead of a major M&A transaction without alerting L2 at all is likely the most effective way to front run any material public disclosure.
We, of course, are not accusing anyone of abusing the system, just pointing out some of the structural variations in dark pool order flow versus regular markets. And as MS points out, it currently trades over 100 million shares per day in just one of its dark liquidity pools. Multiply this by the over 30 providers of such markets and you approach a number that could be more than half the total share volume trades on the NYSE! We hope MS is successful in signing up more clients for MS POOL ahead of what will likely be a substantial crack down on this market, which in this author's belief, is significantly more prone to abuse than the much maligned CDS OTC product.
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