jackie, Do some research on ECN Trading system. You never see the volume on the counters that we monitor. This system is mainly used by the prime brokers, hedges, and mm's. The pinks can also be traded after hours as can all US traded stocks. The volume on this system can be more than the system that we see and monitor. You can start with a google but the SEC has done a position write up that can be found there.
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