What is Gamma Exposure (GEX)? How Options Dealers Influence Markets

Gamma Exposure (GEX) measures the dollar value of hedging required by dealers for a 1% move in the underlying. Learn how GEX dictates market volatility.

Gamma Exposure reveals how option dealer hedging flows create predictable volatility patterns in markets. What is Gamma Exposure (GEX)? It is a metric that quantifies the dollar amount of the underlying asset that option market makers must buy or sell to remain delta-neutral as the price of the asset changes.

Dealers are typically the 'other side' of retail and institutional trades. If the public buys calls, the dealer is short calls. To remain delta-neutral, the dealer must manage their Gamma ($\Gamma$). The aggregate Gamma Exposure is calculated as: $GEX = \sum (\Gamma_i \cdot OI_i \cdot 100 \cdot S^2 \cdot 0.01)$. This represents the change in dealer delta for a 1% move in the underlying price $S$, adjusted for Open Interest ($OI$).

The market behaves differently depending on whether total GEX is positive or negative. This is because the dealer's hedging requirements change directionally based on their net position.

1. Positive Gamma (Long Gamma): Dealers buy as the price drops and sell as it rises. This acts as a stabilizer, suppressing volatility and keeping the price within a tight range. 2. Negative Gamma (Short Gamma): Dealers must sell as the price drops and buy as it rises to keep their delta neutral. This creates a feedback loop that accelerates price moves and expands volatility. 3. The Flip Zone: The price level where aggregate GEX transitions from positive to negative. Below this level, realized volatility typically spikes.

To calculate the total market GEX, we must first calculate the Gamma for each strike. Using the standard Black-Scholes-Merton model Greek formula for Gamma: $\Gamma = \frac{N'(d_1)}{S \sigma \sqrt{T}}$.