Open interest vs volume — what's the difference?
Two numbers that look similar and measure completely different things.
Volume is how many contracts of a specific option traded today. Open interest is how many contracts of that option are currently open — not yet closed out or expired — accumulated over the contract's entire life. A contract can have huge open interest and zero volume today (an old, quiet position nobody is touching), or heavy volume with modest open interest (a lot of today's activity is opening brand-new positions).
Volume: a daily counter
Volume resets to zero at the start of every trading day and counts every contract traded, regardless of whether that trade opened a new position or closed an existing one. It tells you how "active" a contract is right now, but nothing on its own about whether that activity is new interest or existing traders exiting.
Open interest: a running total
Open interest is published once per day (after the exchange's end-of-day clearing) and represents the total number of contracts still open across all holders. It only changes when a trade opens a new contract (open interest rises) or closes an existing one (open interest falls) — a trade between two people who are both closing existing positions actually decreases open interest even though it adds to volume.
Why Volume > Open Interest gets flagged as unusual
If a contract trades more volume today than its entire existing open interest, a large share of today's trading has to be brand-new positioning — mathematically, there simply weren't enough existing contracts for all of today's volume to be closing trades. That combination — a contract with modest standing open interest suddenly seeing volume dwarf it — is one of the most common, simplest "unusual options activity" screens, and it's exactly the flag OptionScope's option chain and scans surface automatically wherever real Volume > Open Interest occurs.
Common mistakes
Assuming Vol>OI always means a directional bet. It flags fresh positioning, not its purpose — it could be a hedge, a spread leg, or a market-maker adjustment just as easily as a speculative bet.
Reading high open interest as bullish or bearish. Open interest measures how much is parked at a strike, not which side initiated it or why — it isn't inherently directional.
Expecting open interest to update intraday. It's an end-of-day figure; if you're watching for real-time unusual activity, volume (and Vol>OI specifically) is the number that moves during the session.
Try it live
The open interest and volume below are real — pulled from OptionScope's live CBOE-fed option chain, with the same Vol>OI flag the app uses. Look up any symbol:
Scan for unusual activity — free →
Related: How to read an option chain · The options Greeks · Implied volatility