Contents
Definition
Open Interest (OI) is the total count of all outstanding (unsettled and unclosed) derivative contracts — futures or options — for a given underlying, strike (for options), and expiry at a specific point in time. Each contract represents one buyer and one seller; OI counts the pair as one contract, not two. OI is reported by NSE and BSE at end-of-day and updated intraday in near-real-time via the exchange's OI data feed. It is distinct from trading volume (number of contracts traded in a session) and is the standard measure of the depth of participation in a derivative instrument. Source: NSE — Derivatives Market Statistics.
How OI Changes
Three transaction types affect OI:
- New buyer + new seller (fresh position): OI increases by 1. Capital is committed on both sides.
- Existing buyer closes by selling to existing seller closing (both exiting): OI decreases by 1. Net open positions reduce.
- Existing position transferred (one party exits, new party enters the same side): OI is unchanged. The aggregate commitment in the market remains the same.
At expiry, all remaining OI is settled (cash for index; physical for single-stock) and OI resets to 0 for that contract.
Market Mechanics
- Market-wide position limit (MWPL): SEBI mandates that total open interest in a single stock's F&O contracts across all participants cannot exceed 20% of non-promoter shareholding. NSE publishes MWPL data daily. When a stock's OI crosses 95% of MWPL, it enters the F&O ban period — no new positions can be opened until OI falls below 80% of MWPL. This is a common and operationally significant constraint for active traders.
- Per-strike OI in options: NSE publishes an options chain showing OI, volume, and premium for every listed strike for a given expiry. This is the most-used OI data format among options traders.
- Change in OI (CoI): The daily change in OI at a specific strike or aggregate level is reported by NSE and used in participant-sentiment analysis.
- Participant-wise OI: SEBI mandates that client category OI (FII, DII, proprietary, retail) be published daily for index futures/options — available on NSE's "Participants wise open interest" page.
Risk Profile
High OI at a strike creates risk for option sellers at that strike — if the underlying reaches it, a large number of contracts need to be settled, and market-makers may not easily hedge a sudden move through a high-OI strike. For option buyers, low OI at a strike means poor liquidity — exiting the position may require accepting a worse price (wide bid-ask spread). SEBI's MWPL framework is specifically designed to prevent excessive leverage concentration in a single stock, which could create disorderly market conditions at expiry. The July 2024 SEBI retail study noted that high aggregate OI buildup in weekly index options — particularly 0DTE strikes — was a contributing factor to the concentrated retail loss pattern, as traders were frequently caught on the wrong side of sharp intraday reversals near expiry.
Worked Example
Nifty 50 options chain for the weekly expiry (next Thursday) shows:
- 24,500 Call OI: 45 lakh contracts; 24,500 Put OI: 38 lakh contracts. Net: Call OI > Put OI at ATM, suggesting more call sellers (shorts) than put sellers — a slight bearish lean in positioning.
- 25,000 Call OI: 120 lakh contracts (highest OI on the call side) — analysts treat this as a significant resistance level because call sellers at this strike would buy the underlying as a delta-hedge if Nifty approaches, potentially capping upside.
- 24,000 Put OI: 95 lakh contracts — treated as support. If Nifty falls toward 24,000, put sellers (who are short puts) may provide demand.
OI alone is not a reliable predictive tool — it describes positioning, not guaranteed outcome. Fast-moving markets can override OI-implied support/resistance in minutes.
Caveats
- OI and volume are frequently confused. OI is the stock (outstanding positions); volume is the flow (daily activity). A high-volume day can occur with declining OI (if mostly closing trades), or rising OI (if mostly opening trades).
- OI data on NSE reflects end-of-day totals by default. Intraday OI from data vendors may be approximate depending on their feed refresh rate.
- The "max pain" theory — that the underlying gravitates toward the strike with maximum option writer profit at expiry — lacks robust statistical support and should not be used as a standalone trading signal.
- Rollover season (last 3–5 days before monthly expiry) produces anomalous OI patterns — near-month OI collapses as positions roll to M+1, which can misread as "bearish unwinding".
See Also
Primary Source
NSE — Derivatives Market Statistics; SEBI Study on F&O Retail Participation, July 2024
MintByte (ARN-314872 / APMI APRN-01658) provides this glossary for educational purposes only. Nothing here constitutes investment advice, a recommendation to buy or sell any security, or a guarantee of returns. Equity and derivatives trading involves risk of loss. Consult a SEBI-registered adviser before making investment decisions.