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Bid-Ask at market open, which comes first? [duplicate]
The options market requires much more attention to avoid the situation you're describing. An overnight $10 ask will remain on the books most likely as Good-Til-Canceled.  The first to bid the low order gets it.  If traders are paying attention, which they probably are then they will bid at $10.  If not, they will bid immediately at $20. If they crossed the order, it would be filled at their higher than $10 bid. This is all governed by the exchange where the ask is posted, and most implement price-time priority.