Wall Street’s ‘Private Rooms’ Are Making Dark Pools Even Darker

Wall Street’s infamous dark pools are getting even darker.

A decade after being engulfed by a controversy that culminated in multiple enforcement actions and a regulator clampdown, these off-exchange trading platforms are touting a way to buy and sell stocks that’s even more opaque.

They’re offering what are dubbed private rooms, gated venues that take the core benefit of a dark pool — the ability to hide big equity deals so they won’t impact prices — and add exclusivity, specifying exactly who can partake in any trade.

Created within the dark pools themselves, the rooms are independent from one ...