Total Open Interest not closed by the end of the session. It differs from Volume: OI reflects cumulative interest, Volume reflects today's activity. When OI rises, new positions are being opened.
What it counts
Open Interest (Open Interest) is the number of contracts that are still outstanding, neither closed nor expired. It is the live stock of positions at a given strike and expiration. It updates once each night, not in real time, so it is a picture of what was built up through yesterday's close.
Why it is the backbone of structural reading
The distribution of open interest across strikes is the raw material for every positioning map. The big pile-ups become the call and put walls, and from them we compute dealer gamma, its flip point and Max Pain. Without this column, those tools don't exist.
Reading it with volume
Open interest that rises after a heavy-volume session means new positions. A fall after it means closing and rolling. Holding steady on huge volume means the session was a handoff between hands, not a build. Volume alone can never tell these three cases apart.
Hypothetical example
Strike 5,000 on an index holds 80 thousand open calls while its neighbors sit tens of thousands lower. That pile-up is what makes 5,000 a wall. The hedging of its sellers holds back an advance toward it, and a break through it releases that restraint all at once.
Common mistake
Reading large open interest as "bullish interest" every time: each open contract has a seller and a buyer, and the number does not say which side started it. The structure (where it piles up) says more than absolute volume.
Where to see it on the platform
The Options Chain shows it for every contract. The Gamma dashboard turns its distribution into walls and a drawn flip point, and the expiration calendar tracks how it rebuilds after each expiry.
