OI vs Volume:
What Each Metric Reveals
Open interest and volume both appear in every option chain, yet most beginners confuse them. They measure different things and together paint a far richer picture than either alone.
The core distinction
Every time you look at an option chain, you see two activity columns side by side: volume and open interest (OI). They feel similar but measure fundamentally different things.
- Volume — the number of contracts traded during the current session. It starts at zero when the market opens and accumulates through the day. At end of session it is reported and then reset for the next day.
- Open interest — the number of contracts that are still open (not yet squared off, exercised or expired) at end of the previous day. It does not reset; it is a running total that increases when new contracts are created and decreases when positions are closed.
Think of it this way: volume is a flow metric (how much traded today?); OI is a stock metric (how much is outstanding?).
How OI changes
OI increases by one contract when a buyer and a seller both open a new position. OI stays flat when an existing holder sells to a new entrant (one position transfers; nothing is created or destroyed). OI decreases when both sides of a trade are closing — a long squares off against a short.
The change in OI column in the option chain shows the net movement from the previous session. A large positive change in OI at a strike means a significant number of new contracts were written there — fresh positional commitment. This is the column that powers buildup analysis.
What volume tells you that OI does not
Volume captures all transactions, including those that net out to zero OI impact. If the same contract is opened and closed four times by different day traders in a single session, volume counts all four trades but OI may end flat. This makes volume a sensitive gauge of intraday interest and liquidity.
High volume at a strike tells you that strike is actively traded right now. A strike with low OI but surging volume may be attracting fresh speculative attention — it can be an early-warning before OI builds. This is especially visible in weekly expiry options, which start life with near-zero OI but can accumulate enormous volume by expiry Thursday.
What OI tells you that volume does not
OI reveals positional commitment across sessions. A strike with massive OI is one where market participants have carried their positions overnight — they have conviction. These strikes are where institutional option writers have sold large quantities, which is why support and resistance levels derived from OI tend to be respected.
OI is also the denominator of PCR (Put-Call Ratio) and the input to max pain calculations. Neither metric is meaningful if you use volume instead.
Reading them together: four signal combinations
- High volume + rising OI — active trading is creating new open positions. A sustained move here is likely backed by genuine conviction. This is the scenario underlying long or short buildup.
- High volume + flat or falling OI — lots of trading happening but positions are being closed at roughly the rate they are opened. Classic day-trading behaviour; the overall positional weight is not shifting.
- Low volume + rising OI — unusual. OI is being added quietly. Can indicate that a single large player (perhaps an institution) is building a position slowly to avoid signalling intent. Worth watching.
- Low volume + falling OI — the market is losing interest in this strike. Positions are quietly being unwound without replacement. Common in deep ITM or far OTM strikes approaching expiry.
A worked NIFTY example
Suppose NIFTY is trading near 22,500 (hypothetical). At the 22,600 call strike on a Wednesday morning, you see:
- OI: 3,20,000 contracts (up 45,000 from Tuesday)
- Volume so far: 68,000 contracts
- LTP (premium): dropped from ₹85 to ₹70
OI is rising sharply (45,000 fresh contracts since yesterday). Volume is already high by mid-session. Premium is falling despite the volume. This pattern — premium falling, OI rising — tells you the new contracts are being opened by sellers (call writers). With NIFTY near 22,500, writers at 22,600 are betting the index stays below that level before Thursday expiry. Each lot is 75 units, so 45,000 new contracts = 33.75 lakh shares of notional exposure added at that one strike in one day.
Now compare the 22,400 put: OI is flat, volume is thin. Nobody is actively positioning at that strike today — the action is entirely at 22,600 on the call side.
Practical tips for NSE/BSE traders
- NSE publishes end-of-day OI on the official OI page; intraday OI from data vendors is estimated and may differ slightly from the official end-of-day figure.
- In the last hour before expiry, volume explodes as positions are squared off. Do not mistake expiry-day volume spikes for fresh conviction.
- SPAN margin requirements on NSE are calculated on OI, not volume. Margin calls are a positional concept, not an intraday one.
- Bank Nifty and NIFTY option chains have the highest OI concentration; individual stock options are far less liquid and OI numbers need to be interpreted in that context.
Common mistakes
- Using volume as a proxy for OI when calculating PCR or max pain — these require end-of-day OI.
- Assuming that a high-volume strike is necessarily a high-OI strike — they diverge frequently on expiry day.
- Ignoring volume entirely and only reading OI — volume catches early activity before OI confirms it.
- Comparing today's OI to yesterday's volume (or vice versa) — always compare like with like across the same session and metric.
Frequently asked questions
What is the difference between OI and volume in options?
Volume is the total number of contracts traded during a session — it resets to zero every day. Open interest is the number of contracts that remain open at end of day — it carries over. Volume tells you today's activity; OI tells you the accumulated positional weight.
Can volume be higher than OI?
Yes. Volume can exceed OI in a single session. This happens when the same contracts are traded multiple times intraday. High volume with flat or falling OI typically means day traders are active but positional players are not building fresh exposure.
Why does OI matter more near expiry?
Near expiry, large OI concentrations at specific strikes exert gravitational pull on price — known as max pain or pin risk. Writers who have sold large quantities of options at those strikes have incentives to keep price near those levels. Volume spikes on expiry day also signal accelerated position squaring.
What does high volume but low OI mean?
High volume with low OI suggests intense intraday trading activity without much positional commitment. Traders are opening and closing within the same session rather than carrying overnight risk. This is common in very liquid ATM strikes near weekly expiry.
See OI and volume side by side, live
TradePulse displays real-time OI, change in OI, and volume for every NIFTY and Bank Nifty strike on the same screen.