Two scenarios that play out regularly re. option volume and open interest data. I draw my conclusions and would like to know if these are correct. It all seems pretty straightforward but perhaps I am overlooking some triviality. Anyone willing to take a look and comment: thanks in advance. All numbers refer to strictly one option series (one particular contract, put or call, that doesnât matter). One note: Open interest of course is reported the next day. So âDay 1 OIâ means open interest as reported on Day 1, which represents open interest of Day 1 BEFORE market open. âDay 2 OIâ represents open interest as reported the next day, which is equivalent to open interest of Day 1 AFTER market close. Just to avoid confusion. Scenario 1: Day 1: Volume = 200 OI = 1000 Day 2: OI = 1300 Conclusion: This is impossible. Volume 200 cannot create an OI change of +300. These data MUST be wrong. Scenario 2: Day 1: Volume = 200 OI = 1000 Day 2: OI = 700 Conclusion: This is possible, assuming at least 100 contracts were exercised after market close on Day 1. These would represent the âmissingâ -100 OI change that volume does not account for. (btw in that case all 200 Volume must have been CLOSing positions). Of course, these cases refer to any day in an option life except expiration day. Also, we donât assume contract adjustments due to stock splits, dividends etc. Basic stuff huh? Willing to take a beating if Iâm missing the obvious. Thanks!