SPX Net GEX Explained: Gamma Exposure, 0DTE & Trends
The S&P 500 options market has grown so large that it now shapes how the index itself behaves. SPX net GEX โ net gamma exposure โ measures how dealers are positioned and tells you whether their hedging is likely to calm the market or amplify its moves. Here is what gamma exposure is, how to read an SPX GEX profile, and why 0DTE options changed the picture.
What is GEX in trading?#
GEX stands for Gamma Exposure. It estimates the total gamma carried by options dealers (market makers) across all strikes and expirations of an underlying. Dealers are in the business of providing liquidity, not making directional bets, so they hedge the options they hold by buying and selling the underlying to stay delta-neutral. Gamma dictates how much that hedge must change as price moves โ and the sign of net gamma determines whether their hedging pushes price back toward a level or chases it away.
Positive vs negative gamma regimes#
The single most useful thing GEX tells you is which regime the index is in. The two behave very differently:
| Positive GEX (long gamma) | Negative GEX (short gamma) | |
|---|---|---|
| Dealer hedging | Sells rallies, buys dips | Buys rallies, sells dips |
| Effect on price | Dampens moves โ mean reversion | Amplifies moves โ trend & acceleration |
| Typical volatility | Lower, range-bound | Higher, prone to air pockets |
| What to watch | Pinning near big strikes | Fast moves once the flip breaks |
Illustrative regime read
Reading an SPX GEX profile#
A GEX profile plots net gamma by strike. Positive bars (call-dominated, in green) mark levels where dealers sell into strength and buy weakness โ magnets and walls. Negative bars (put-dominated, in red) mark levels where hedging accelerates moves. The illustrative SPX profile below shows the structure traders look for:
SPX net GEX by strike โ illustrative
GammaBaba renders this same structure as a colour heatmap across strikes and expirations, so the key GEX levels โ the King Strike, the call and put walls and the gamma flip โ are visible at a glance for SPX, SPY or any optionable ticker.
The gamma flip level#
The gamma flip is the price where net dealer gamma crosses zero. Above it the index is usually in a positive-gamma, mean-reverting regime; below it dealers are short gamma and their hedging amplifies moves. That is why selloffs that break the flip so often accelerate โ the hedging flow flips from stabilising to destabilising. Knowing where the flip sits is one of the highest-value reads GEX offers.
Why 0DTE changed SPX gamma#
Same-day (0DTE) options now make up a large share of SPX volume, and their gamma is enormous because gamma peaks as expiration approaches. That concentrates a huge amount of hedging sensitivity into the current session โ and it can evaporate at the close as those options expire. The illustrative term structure below shows how lopsided net gamma can be toward the front:
SPX net GEX by expiration โ illustrative
For a deeper look at the mechanics and risks of same-day options, see 0DTE Options Risk and the docs guide on 0DTE & GEX.
Track SPX net GEX on GammaBaba#
GammaBaba computes gamma exposure across the full US options universe and refreshes it through the session. Open the SPX heatmap for the strike-by-strike picture, drop into the GEX Profile for the net-by-strike view, or use Compare to line SPX up against SPY, QQQ and IWM.
Frequently asked questions
What is SPX net GEX?
SPX net GEX (net gamma exposure) is an estimate of the total gamma options dealers carry across all S&P 500 index option strikes and expirations. Its sign indicates whether dealer hedging is likely to dampen index moves (positive gamma) or amplify them (negative gamma), and its distribution by strike reveals magnets and walls.
What does positive vs negative GEX mean?
In positive (long) gamma, dealers sell rallies and buy dips, which dampens volatility and encourages mean reversion. In negative (short) gamma, dealers buy rallies and sell dips, which amplifies moves and raises volatility. The crossover point is the gamma flip.
What is the gamma flip level?
The gamma flip is the underlying price at which net dealer gamma crosses from positive to negative. Above it the market is usually stabilising; below it dealer hedging tends to accelerate moves, which is why breaking the flip often speeds up a selloff.
Why does 0DTE matter for SPX gamma?
Gamma is largest right before expiration, so same-day (0DTE) options carry outsized gamma. Because 0DTE is now a big share of SPX volume, a large amount of hedging sensitivity is concentrated in the current session and can disappear at the close, making intraday moves increasingly sensitive to near-term positioning.
Where can I see SPX gamma exposure?
GammaBaba shows SPX gamma exposure as a strike-by-strike heatmap and a net GEX profile, with the King Strike, call and put walls and the gamma flip marked. You can also compare SPX against SPY, QQQ and IWM side by side.