Another possibility for the heavy volume in WoldCom shares comes from inter-trader transactions. Rick Black, an analyst with Blaylock & Partners, says some traders exchange shares of stock between each other -- in effect swapping large amounts of cheap stock for smaller amounts of a more valuable stock -- instead of putting the shares out into the open market. The exchanged shares still get counted as part of a stock's overall volume.

Black estimates that about one-third of WorldCom's shares on Wednesday moved in such a manner.