Gamma Exposure

What is Gamma Exposure?

Gamma exposure (GEX) estimates how much option dealers' hedging must respond to price movement. Gamma is the rate at which an option's delta changes as the underlying moves; aggregate exposure is estimated by multiplying each listed option's gamma by its open interest and contract multiplier, then summing across strikes and expirations. Open interest does not reveal who is long, so the common convention assumes dealers are long the calls and short the puts their customers trade, making the call side contribute positive gamma and the put side negative.

The sign of the total matters. When dealers are net long gamma, staying delta-neutral forces them to sell as price rises and buy as it falls, which tends to dampen moves and can pin price near heavily traded strikes (option strike walls). Net short gamma reverses that: hedging chases price and can amplify moves. The zero-gamma flip is the estimated spot level where the regime changes. All of it is inference from assumptions, not an observed dealer book, and vendor estimates disagree.

How traders use it

• As a volatility-regime read: positive-gamma conditions favor range and mean-reversion tactics, while negative-gamma conditions warrant trend-following posture and wider stops; most traders pair the read with implied volatility for fuller context.
• As a levels framework: large-gamma strikes and the zero-gamma flip are mapped as zones where hedging pressure may pin or release price, especially into large expirations when that exposure rolls off.
• As a positioning cross-check: a net number built from heavy put buying tells a different story than the same number built from call overwriting, which is why GEX is often read next to the put/call ratio.