Thanks appreciate it! So sounds like then Globex and Open outcry are separate markets then although they are closely correlate as they trade the same asset but

Thanks appreciate it! So sounds like then Globex and Open outcry are separate markets then although they are closely correlate as they trade the same asset but aren't obligated to reroute orders. As for options, AFAIK, CBOE and ICE already keep multi-legged books in electronic trading. For example, you can request for a multi-leg order via Interactive Brokers and it'll return a bid/ask spread that's the sum of all your ratio's/legs. When you execute, I think IB's SmartRouter does the magic to figure out which exchange to submit your order to (whether to submit it all to a multi-leg book or as single orders; but IB is on the hook to guarantee the complete execution of your order). On liquid options, hitting mid on your multi-leg has a decent chance of being executed. However options in general are not as liquid as equity, so happy that guys at CBOE/CME can still do open outcry.