What is Open interest (OI)?
What Is Open Interest in Options?
Updated 2026-07-21
Quick answer
Open interest is how many options contracts remain open. Unlike volume, it does not reset each morning and usually updates after the session.
Also called: OI, open interest options.
Visual explainer
Open interest is contracts still open. Volume is only today’s trades. OI usually updates after the session; the tape is live.
Full definition
Volume counts contracts traded today. OI counts contracts still outstanding. Rising OI with heavy volume often suggests new positions; falling OI can mean closing or rolling. Use OI for walls and overnight commitment, not for same-second decisions.
How it shows up in TradingFlow
- Option Chain Analysis
Strike-level OI for call/put walls and structure.
- Learn: Option Chain & OI
Tutorial on OI, Vol/OI, ΔOI, and walls.
How to read it
- Use OI for structure (walls), not for same-second decisions.
- After large flow, check next-day ΔOI when available.
- Combine with Vol/OI for freshness: high volume vs standing OI.
Who this is for
Traders checking whether activity looks like new positioning versus day-trading churn.
Common mistakes
- Confusing OI with volume.
- Expecting OI to update tick-by-tick like the live tape.
Frequently asked questions
- When does open interest update?
- Typically after the trading day (exchange/vendor lag). Use live volume and flow intraday; use OI for overnight structure and confirmation.
Related terms
- Volume / open interest (Vol/OI)Vol/OI is today’s volume divided by open interest. High ratios mean today’s trading is large versus the standing book.
- Call wallA call wall is the strike above spot with the densest call open interest or call-side gamma. Traders often treat it as resistance when dealers hedge.
- Put wallA put wall is the strike below spot with the densest put open interest or put-side gamma. Traders often treat it as support when dealers hedge.
- Unusual options activity (UOA)UOA flags contracts or underlyings trading far above recent norms in volume, size, or premium. It is an attention screen, not a directional signal.
More guides
See the workflow in TradingFlow
Open the live Option Trades tape, rank unusual activity, and validate structure in one research path.