Whether this is illegal depends on your jurisdiction. In the US, running a prediction market on US-listed stocks is very illegal. I'm not clear whether it's ill

Whether this is illegal depends on your jurisdiction. In the US, running a prediction market on US-listed stocks is very illegal. I'm not clear whether it's illegal to participate in one, even as an insider (this is not legal advice). In Europe you can run a shadow stock market like this - currently CFDs are the popular way to do it - but it's generally illegal to insider trade on one.