Summary. Dealer positioning is shorthand for the aggregate state of the option books held by the firms that make markets in listed options. Dealers earn the bid-ask spread rather than betting on direction, so they hedge what they absorb. This guide explains why that hedging is systematic, which parts of the book matter, how to read the sign of dealer gamma and how far public estimates can be trusted.
1. Why dealers hedge
Listed options in the US are made largely by a concentrated group of electronic market-making firms. They quote both sides, earn the spread and absorb whatever customers want to trade, which leaves them holding positions they did not choose.
Suppose a customer buys an SPX call from a dealer. The dealer is now short the call and loses money if the index rises. To offset that, it buys index exposure, usually E-mini S&P 500 futures, SPY shares or a basket of the underlying stocks. That trade is the delta hedge. The hedge must then change with price (gamma), with time (charm) and with implied volatility (vanna).
Dealers net offsetting positions and do not hedge every trade instantly, but risk limits and capital requirements make large unhedged positions costly. In aggregate their hedging is therefore systematic and partly estimable from public data, and it is the hedging, not any opinion, that moves prices around heavily traded strikes.
2. The dealer book is not a single number
The dealer book is better read as a set of related sensitivities than as one position:
- Net delta (DEX). The dollar delta of the options dealers hold, which their hedges currently offset. DEX gives the size of the existing hedge; flows come from changes in it.
- Net gamma (GEX). How quickly that delta changes as price moves, and so how much dealers must trade per move. Its sign sets the intraday character of a session.
- Net vega. Exposure to changes in implied volatility. A short-vega book loses when volatility spikes, which can force dealers to cut risk at the worst moment.
- Net vanna. How delta changes with implied volatility. Under the usual convention, rising volatility gives the out-of-the-money puts dealers are short more delta, so dealers must sell the underlying, which can feed a volatility-up, price-down loop in stress. Falling volatility reverses it.
- Net charm. How delta changes as time passes. Charm grows as expiry approaches and can be a large share of hedging flow in the days and hours before a big expiration.
- Higher-order Greeks. Speed (how gamma changes with price) and color (how gamma changes with time) are third-order effects. They matter mainly for same-day options and around scheduled events.
These can reinforce or offset each other, so a full read considers them together. The DataFirst terminal shows gamma, delta and vanna exposure (GEX, DEX and VEX) by strike. For the two main second-order flows, see vanna vs charm.
3. How to read the sign of the book
The most useful single question about positioning is whether dealers are long or short gamma right now.
When dealers are long gamma (positive GEX), rebalancing flow opposes each move: they sell as price rises and buy as it falls, which tends to pull price back toward heavily held strikes. Realized volatility tends to compress and daily ranges to narrow, and Barbon and Buraschi find that positive dealer gamma goes with intraday reversal.
When dealers are short gamma (negative GEX), rebalancing flow follows the move: they sell into weakness and buy into strength. Realized volatility tends to expand and moves persist. Baltussen, Da, Lammers and Martens link short-gamma hedging by option dealers and leveraged ETFs to intraday momentum into the close across a broad set of futures markets.
The sign is a regime, and it can change within a session. Open interest is published once per day, but gamma also depends on price, implied volatility and time. A market that opens long gamma with the gamma flip just below can turn short gamma after a modest decline, so a prior-close estimate can be out of date by midday.
4. Where positioning sits, strike by strike
The aggregate sign matters for the session as a whole; the distribution across strikes matters for specific price levels. Large dealer gamma at one strike forms a wall, because hedging intensifies as price approaches it and as expiry nears.
Under the usual convention the two walls are built differently. The call wall, the strike with the largest positive net GEX, concentrates dealer-long call gamma whose hedging sells into rallies, so it acts as resistance. The put wall, the strike with the largest negative net GEX, concentrates dealer-short put gamma whose hedging sells into declines. When it acts as support, that comes mostly from put holders taking profits near the strike, which lets dealers unwind their short hedges.
On a GEX-by-strike chart, the tallest positive bar is the call wall and the deepest negative bar is the put wall. The gamma flip cannot be read off where the bars change sign: it comes from recalculating total GEX at hypothetical prices and finding the zero crossing, so it often lies between strikes. See GEX levels explained.
5. Limits of dealer positioning as a concept
Real dealers hedge across several instruments, on different schedules, and offset risk against positions public data does not show. Public estimates rely on open interest and a sign convention that treats dealers as long index calls and short index puts. That is broadly consistent with evidence that customers tend to write index calls and buy index puts, but it can be wrong at any single strike, particularly after heavy customer call buying. GEX is a directionally useful map, not a precise measurement.
What public data can show with reasonable confidence is whether aggregate dealer hedging is likely stabilizing or amplifying, where the largest concentrations of hedging flow sit, and how they shift between expirations. That is context for reading price action, not a signal on its own. For how the hedging is carried out, see options market maker hedging.
For educational and informational purposes only. Not financial advice. Options trading involves substantial risk of loss.