Open Interest (OI)
The total number of outstanding contracts at a strike that haven't yet been closed, exercised or expired.
Open interest vs volume, at a glance
- Open interest
- Positions still opencumulative — carries over between sessions
- Volume
- Contracts traded todayresets to zero each session
- OI rises
- New money enteringfresh positions being opened at that strike
- OI falls
- Positions closingexisting exposure being unwound or expiring
- OI unchanged, volume high
- Churnpositions changing hands, not net new exposure
One contract requires both a buyer and a seller, so open interest counts the position once, not twice — a strike showing 5 lakh OI has 5 lakh contracts outstanding, not 10 lakh.
OI measures how many positions exist, not how many trades happened today (that's volume) — a strike can have huge OI with barely any volume on a quiet day. Reading OI alongside price direction is what separates genuine buildup from noise: see OI Buildup Matrix for how DeltaK and most active traders classify the four combinations.
Example: a strike showing 5 lakh contracts of OI but only 2,000 traded today has a lot of standing exposure and little fresh activity — a strike with just 1 lakh OI but 50,000 traded today is seeing far more real, active repositioning, even with a fraction of the total OI.
Frequently asked
What does OI mean in the option chain?
Open interest — the number of contracts at that strike that are still open, meaning they have not yet been closed out, exercised or expired. It measures how much standing exposure exists at a strike, which is different from how much trading happened there today.
What is the difference between OI and volume?
Volume counts contracts traded during the session and resets to zero the next day. Open interest counts positions still outstanding and carries over. A strike can show large OI with almost no volume on a quiet day, and large volume with flat OI when positions are simply changing hands.
What does rising call OI mean?
New call positions being opened at that strike. Read alongside price it separates buildup from unwinding: call OI rising while price falls is conventionally read as call writing — sellers treating that strike as resistance — whereas call OI rising with price is read as fresh long buildup.
Is high open interest bullish or bearish?
Neither on its own. High OI marks a strike that matters — where the most exposure sits, and often where price gravitates near expiry — but the direction of the signal comes from pairing the OI change with the price change, not from the OI level by itself.
Related terms
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