Options Basics
What Is Open Interest (OI) in Options Trading?
Open Interest is the total number of outstanding (not yet closed) option or futures contracts for a strike and expiry. Reading how OI changes alongside price is one of the fastest ways to gauge whether new money is entering or leaving a position.
Updated 2026-09-15 · 5 min read
Open Interest (OI) is the total number of derivative contracts — options or futures — for a given strike and expiry that are currently open, meaning they haven't yet been closed out, exercised, or expired. Every time a buyer and a seller create a brand new position, OI increases by one contract. Every time an existing position is closed (a buyer sells to close, or a seller buys to close), OI decreases by one. If a buyer and seller simply trade an existing contract between themselves without creating a new one, OI stays flat even though volume ticks up.
Open Interest vs. Volume
Volume counts every trade executed during the day, reset to zero each session. Open Interest is a running, cumulative total of contracts still outstanding — it only changes when positions are opened or closed, and it carries over from one day to the next. High volume with flat OI usually means existing positions are simply changing hands; rising volume alongside rising OI usually means fresh positions are being built.
Why OI buildup matters
Because OI only moves when a position is opened or closed, tracking OI change alongside price direction tells you whether a price move is being driven by fresh conviction (new positions) or by existing positions unwinding. Traders generally classify the combination of price direction and OI direction into four buildup patterns:
- Long Buildup — price rises and OI rises. New buyers are entering; considered a bullish signal.
- Short Buildup — price falls and OI rises. New sellers (writers) are entering short positions; considered a bearish signal.
- Short Covering — price rises and OI falls. Existing short sellers are buying back to close; often produces a sharp upward move as shorts exit.
- Long Unwinding — price falls and OI falls. Existing long holders are selling to close; a weakening of a prior bullish move rather than fresh bearish conviction.
Reading OI on an option chain
On a live option chain, OI is shown per strike, separately for calls and puts. Strikes with unusually high Call OI are often watched as potential resistance, since a large number of call writers have effectively sold the right for the underlying to rise past that strike without giving up premium. Symmetrically, strikes with unusually high Put OI are often watched as potential support. This is a heuristic, not a guarantee — OI concentration reflects where market participants have taken a view, not a hard price ceiling or floor.
OI is most informative when read together with the day's OI change (not just the absolute level) and with price action at that strike, across the full session rather than a single snapshot.
Frequently Asked Questions
Does high Open Interest mean a stock will move a lot?
Not by itself. High OI means a lot of outstanding positions exist at that strike, which can amplify hedging-related flows (like dealer gamma hedging) near expiry, but OI alone doesn't predict direction — it needs to be read alongside price and OI change.
Why does OI sometimes stay flat even when volume is high?
Because volume counts every trade, including trades where one party is opening a position and the other is closing one — those offset and leave OI unchanged. OI only rises or falls on net new position creation or closure.
When does Open Interest reset?
OI for a specific strike and expiry runs until that contract's expiry, at which point all remaining open positions are settled or exercised and OI for that series effectively goes to zero. It does not reset daily the way volume does.
View live Open Interest on the Option Chain on Replete Alpha