Learn · F&O
What is open interest (OI) in F&O and how to read it
Open interest is the total number of derivative contracts still open and not yet closed. It measures outstanding inventory, not whether buyers or sellers initiated the trade.
In one line
Open interest is the total number of outstanding futures or options contracts that have not been closed; every 1 open contract has a matched long and short side, so price and OI together describe inventory and price behaviour but do not identify who initiated, hedged, or profited.
BazaarBaaziSource & method
OI versus volume
Volume counts how many contracts changed hands during the day, and it resets every session. Open interest counts how many contracts are still live, carried from one day to the next, and it only changes when a new position is opened or an existing one is closed. Two traders opening a fresh contract between them adds one to open interest. One closing against another removes one.
OI measures outstanding inventory rather than daily churn. A strike with high OI is therefore a concentrated part of the open book and may become a level traders monitor. It is not proof of support, resistance, writer identity, or the direction in which those positions were opened.
The familiar price-OI grid is a heuristic
Market shorthand labels price up with OI up as long buildup, price down with OI up as short buildup, price up with OI down as short covering, and price down with OI down as long unwinding. Those labels are hypotheses, not identities: aggregate OI has no aggressor, account, opening-versus-closing flag, or linked hedge.
Use the grid only as a prompt for confirmation from price structure, volume, spreads, volatility and, where available, participant-level evidence. It cannot tell you who is behind the move, whether a short is covered, or whether either side made money.
FAQ3 reader questions · AEO-eligible
Common questions on open interest.
What is the difference between open interest and volume?
Volume is the number of contracts traded in a session and resets daily. Open interest is the number of contracts still open and carried over, changing only when positions are newly opened or closed.
Is high open interest bullish or bearish?
Neither on its own. High OI shows a large outstanding matched inventory at a level; it does not identify the initiating side or direction.
What does rising OI with rising price mean?
Traders often call it long buildup, but the public aggregate proves only that price rose while more matched contracts remained open. Direction and strategy need separate evidence.
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