The secret stock market. 'Dark pools' and other new-age exchanges rewrite the rules, under the radar

Liquidnet Holdings Inc., an alternative trading system used by institutions, has just executed a block trade of a million shares or more.

Unlike the bulk of trading in stocks, this trade was made anonymously and was executed outside of the market where retail investors and institutions meet. And unlike a trade on the floor of the New York Stock Exchange, no one will ever know who put a million shares up for sale and who just bought them.

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In a matter of months more than three dozen dark pools have taken shape, creating a new and wild frontier that is largely unregulated. And the industry is growing so fast regulators can't keep up. Moreover, some observers fear these private marketplaces could take too much trading volume from the public markets -- putting retail investors at a disadvantage.

What's certain is dark pools have radically altered the way big institutions trade. And because private trading networks are extremely profitable, an array of old-line Wall Street firms is following in the footsteps of independent startups that have carved out the industry's hottest new niche.

These so-called alternative trading systems are propagating rapidly, are often labeled "dark pools" because of their nebulous and murky nature. Estimated to handle about 1 out 10 shares traded each day in the U.S., dark pools are meeting a need by institutions to grab or dump stocks quietly -- and anonymously. Like Liquidnet, many of them sport imaginative brand names in a nod to science fiction, such as Sigma X, VortEx and Block Alert.


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