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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. Read alongside price, a rise or fall in OI signals whether a move is being backed by fresh money.
In one line
Open interest is the total number of outstanding futures or options contracts that have not been squared off, and read together with price it reveals conviction, since rising price on rising OI signals fresh longs (a strong move) while rising price on falling OI signals short covering (a weaker one).
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.
Because OI measures commitment rather than churn, it is the cleaner gauge of how much money is actually riding on a level. A strike with very high open interest is a strike a lot of participants care about, which is why option OI is used to map likely support and resistance zones for the underlying.
The four price-OI combinations
There is a simple grid the desk reads. Price up with OI up is a long buildup, fresh buyers driving the move, and it is the most reliable bullish signal. Price down with OI up is a short buildup, fresh sellers leaning in, bearish. Price up with OI down is short covering, sellers fleeing rather than buyers arriving, a move that often fades. Price down with OI down is long unwinding, holders booking out.
None of these is a trade by itself. The value is context. A breakout on a long buildup has fuel behind it. The same breakout on short covering may stall once the trapped sellers are done exiting. Pairing the price chart with the OI change turns a one-dimensional move into a read on who is actually behind it.
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 strong participation at a level, and you must pair it with the price move and whether OI is rising or falling to judge direction.
What does rising OI with rising price mean?
It signals a long buildup, where fresh buyers are entering and backing the up-move with new money. It is generally read as the strongest bullish combination.
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