Disclosure: GEX Levels sells options-flow and gamma-exposure education products, including the Education Library and GEX Indicator. This article is educational only — not financial advice.
How to Read an Options Chain: A Plain-Language Guide for Traders
An options chain is a grid that lists every available options contract for a specific stock or ETF — organized by expiry date and strike price, with calls on one side and puts on the other. Once you can read one fluently, it becomes one of the most information-dense tools in market analysis. This guide walks through every column and shows how chain data connects to flow analysis and GEX structure.
The Basic Structure of an Options Chain
When you open an options chain on any platform (thinkorswim, IBKR, Tastyworks, Robinhood, etc.), you see a grid organized around two axes:
- Expiry date — each expiration is a separate section. You select the expiry you want to view: today (0DTE), this Friday (weekly), end of month (monthly), or further out (quarterly, LEAPS).
- Strike price — running down the center column, from lowest to highest. The current stock price sits roughly in the middle, with in-the-money (ITM) options above and below it and out-of-the-money (OTM) options further out.
Calls are typically displayed on the left side of the chain; puts on the right. For any given strike, you can see both the call and the put simultaneously.
The row where the stock is currently trading is highlighted — this is the at-the-money (ATM) line. Everything between the ATM line and the edges is either ITM (in the money) or OTM (out of the money).
What Each Column Means
| Column | What it shows | Why it matters |
|---|---|---|
| Bid | Highest price a buyer will pay right now | Selling at the bid = immediate fill, worst price |
| Ask | Lowest price a seller will accept right now | Buying at the ask = immediate fill, worst price |
| Mid | Midpoint of bid and ask | The "fair" price for limit orders; most fills land near here |
| Last | Price of the most recent trade | Can be stale in illiquid strikes — bid/ask is more current |
| Volume | Number of contracts traded today | High volume = active market; low volume = illiquid, wide spreads |
| Open Interest (OI) | Total outstanding contracts not yet settled | Structural positioning; raw input to GEX calculations |
| IV (Implied Volatility) | The market's forward expectation of price movement, in annualized % terms | Higher IV = more expensive options; varies by strike (skew) |
| Delta | How much the option price moves per $1 change in the underlying | Directional sensitivity; approximately = probability of expiring ITM |
| Gamma | How much delta changes per $1 change in the underlying | Critical for GEX — this is the number that gets multiplied by OI |
| Theta | Daily time decay — how much the option loses per day all else equal | Sellers collect theta; buyers pay it. Accelerates near expiry |
| Vega | Sensitivity to a 1% change in IV | High vega = option price moves a lot when IV changes |
In-the-Money vs. Out-of-the-Money: What to Look For
Calls are in the money (ITM) when the stock price is above the strike. A 150 call when the stock is at 160 is $10 ITM — it has $10 of intrinsic value. Calls are out of the money (OTM) when the stock price is below the strike. A 170 call when the stock is at 160 is $10 OTM — pure time value, no intrinsic value.
Puts are the reverse: ITM when stock is below strike, OTM when stock is above strike.
Why this matters for reading the chain: ITM options are more expensive but move more like the underlying (higher delta). OTM options are cheaper but require a larger move to profit. The concentration of open interest in ITM vs OTM strikes tells you about the positioning strategy in use — income sellers tend to concentrate near ATM; directional speculators often go OTM for leverage.
Open Interest: The Most Important Column for GEX
Open interest is the total number of contracts that exist and haven't been closed or exercised. It accumulates over time as new positions are opened. Unlike volume (which resets daily), OI persists — it's a record of positioning built up over days or weeks.
When you look at a chain and see 50,000 contracts of OI at the 560 strike on SPY calls, that represents 50,000 outstanding call contracts — each covering 100 shares. Whoever sold those calls (typically dealers acting as market makers) must hold a corresponding position and delta-hedge it dynamically.
Gamma Exposure (GEX) is calculated by multiplying gamma × open interest × 100 (shares per contract) × spot price at each strike, then summing across all strikes. The strikes with the highest OI and highest gamma are where dealer hedging flows will be most intense — which is exactly where GEX structural levels (Call Wall, Put Wall, Gamma Flip) form.
Reading OI on the chain directly lets you identify these levels without needing a dedicated GEX tool — look for the strikes with the highest OI concentration, especially for near-term expirations where gamma is amplified.
Volume vs. Open Interest: The Key Distinction
Beginners often conflate volume and OI. They measure different things:
- Volume: contracts traded today. High volume on a strike means lots of activity — but it doesn't tell you if it's new positions or closing old ones.
- Open Interest: contracts that exist and are open. It changes only when new positions are opened (OI increases) or existing ones are closed/expire (OI decreases).
If a strike shows 10,000 volume but OI only increases by 2,000 the next day, most of that volume was opening and closing within the session — not new sustained positioning. If OI increases by 9,000, nearly all the volume was new positions being built.
For flow analysis: when a large sweep prints and OI increases significantly at that strike the next session, the position is confirmed as new/opening. If OI doesn't move, the sweep may have been closing activity.
Implied Volatility Skew: What the Chain's IV Column Reveals
If you scan down the IV column across strikes, you'll notice IV is not constant. It varies by strike — and this variation is called the volatility skew (or smile).
In equity markets, IV is typically highest for OTM puts (far below current price) and lower for OTM calls. This skew reflects demand: investors and institutions buy downside protection (OTM puts) more than upside calls, bidding up their IV. The steeper the put skew, the more the market is paying for tail-risk protection.
When the skew inverts — when OTM calls carry higher IV than OTM puts — it signals unusual demand for upside exposure. This is rare and often associated with specific catalysts (M&A rumors, earnings surprises, sector rotation).
Reading IV skew from the chain is a quick way to understand the market's directional lean without needing a separate tool.
Practical Chain Reading: A 60-Second Scan
When you open a chain for a ticker you want to analyze, here's a structured scan:
- Select the most active expiry — usually the nearest weekly or monthly with significant OI. This is where dealer exposure is most concentrated.
- Find the ATM strike — the highlighted row nearest to current price. Note the bid/ask spread: tight = liquid, wide = illiquid.
- Scan OI across strikes — identify the 2–3 strikes with the highest OI concentrations on both calls and puts. These are your structural levels.
- Check IV at those strikes — elevated IV at a specific strike means the market expects significant activity near that price.
- Note volume vs. OI — is today's volume building new OI or trading existing positions? Tomorrow's OI change will tell you.
This five-step scan takes under a minute and gives you the structural context for any options flow that prints on that name during the session.