I assume you're talking about stock options, not actual stock. Most stock option grants don't allow any transfer of ownership without at least the approval of

I assume you're talking about stock options, not actual stock. Most stock option grants don't allow any transfer of ownership without at least the approval of the company who issued stock options. So given the current rules for stock options such trading is not possible. Were the rules to change, it would still be highly problematic because you're essentially creating a stock exchange and those are highly regulated by the government (since without oversight they are great avenues for fraud).