What Is Options Open Interest and Why It Matters
Open interest (OI) is the total number of outstanding options contracts that haven't been closed, exercised, or expired. It tells you how many contracts are currently "alive" at a specific strike price and expiration.
It's one of the most misunderstood metrics on the options chain, but it directly impacts how easily you can enter and exit trades.
Open Interest vs. Volume
These two numbers appear side by side on every options chain, and they measure different things:
Volume = the number of contracts traded today. It resets to zero each morning.
Open Interest = the total number of contracts currently open. It updates once per day, after the close.
| Metric | Measures | Resets | Updates |
Example:
Volume was 2,000 but OI didn't change because the new openings and closings netted out.
How Open Interest Changes
Open interest increases when a new buyer and a new seller create a fresh contract. Both sides are opening new positions.
Open interest decreases when an existing holder sells to another existing holder who is closing their position. Both sides are closing.
Open interest stays the same when a new trader takes over an existing position (one side opens, the other closes).
Why Open Interest Matters
1. Liquidity Indicator
High open interest at a strike means many participants hold contracts there. This typically produces:
Low open interest means fewer participants. You'll face wider spreads, harder fills, and potentially unfavorable pricing.
Rule of thumb: Look for strikes with OI above 500-1,000 contracts for standard trades. For large positions, you want OI in the thousands.
2. Support and Resistance Levels
Large concentrations of open interest at specific strikes can act as magnets for the stock price near expiration. Market makers who sold those options need to hedge, and their hedging activity can pin the stock near high-OI strikes.
If the $100 strike has 50,000 contracts of open interest (both calls and puts combined) while surrounding strikes have 5,000, the stock has a tendency to gravitate toward $100 as expiration approaches. This isn't guaranteed, but it's a real effect driven by dealer hedging flows.
3. Sentiment Gauge
Rising OI + rising prices = new money flowing into bullish bets. Confirms the trend. Rising OI + falling prices = new money flowing into bearish bets. Confirms downward pressure. Falling OI + rising prices = short sellers closing (covering). Rally may be fragile. Falling OI + falling prices = long holders closing (liquidating). Selling pressure may be exhausting.
This four-way grid gives you a framework for interpreting whether price moves are backed by new conviction or just position unwinding.
4. Expiration Risk Assessment
High open interest at your strike near expiration increases the chance of pinning and unpredictable behavior on expiration Friday. If you hold a position at a high-OI strike heading into the final day, consider closing before 3:00 PM to avoid assignment surprises.
Reading OI on the Options Chain
When scanning an options chain:
Practical Application
Before entering any options trade, check that the strike and expiration you're targeting have sufficient open interest. This is especially important for less liquid stocks where spreads can be wide enough to eat into your profit.
A $2.00 option with a $1.90 bid and $2.10 ask (10% spread) is far more forgiving than a $2.00 option with a $1.60 bid and $2.40 ask (40% spread). Open interest is your best predictor of which scenario you'll face.