SPX Gamma Exposure

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What Is SPX Gamma Exposure (GEX)?

SPX Gamma Exposure (GEX) measures the aggregate gamma positioning of options dealers in the S&P 500 (SPX). It estimates how market makers must hedge as price moves, which can create either stabilizing or amplifying flows in the underlying index.

When SPX Gamma Exposure is positive, dealers are typically long gamma and hedge by selling into strength and buying into weakness — this can dampen volatility and support range-bound trading. When SPX Gamma Exposure is negative, dealers are short gamma and hedge by buying strength and selling weakness — which can accelerate moves and increase volatility.

Quick Answer:

SPX Gamma Exposure shows whether dealer hedging flows are likely to stabilize or amplify market moves. Positive GEX tends to suppress volatility. Negative GEX tends to increase volatility.

This is a standard net gamma curve, using basic assumptions that options liquidity providers are short put options and long calls. In particular it can be used as a map which allows traders to quickly estimate where large put and call positions are located in the market.

Standard Gamma Curve as Volatility Estimate

Standard gamma curves are based on a set of simple assumptions intended to describe how options dealers are positioned in the market. The size of these positions have been statistically linked to future or forward volatility.

These curves are a small fraction of what SpotGamma monitors to gain an understanding of the options impact on stocks.

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FAQ: SPX Gamma Exposure

1. What does positive SPX GEX mean?

Positive SPX GEX suggests dealers are long gamma and likely to hedge in ways that reduce volatility.

2. What does negative SPX GEX mean?
Negative SPX GEX indicates dealers are short gamma and may hedge in ways that amplify market moves.

3. Why does SPX GEX affect volatility?
Dealer hedging activity can create systematic buy/sell pressure as price moves, influencing short-term volatility.

4. Is SPX GEX predictive?
GEX is not a guarantee of direction, but it provides context for how price may behave in different volatility regimes.

5. How often is SPX GEX updated?
The SPX Gamma Exposure chart is updated daily using current options positioning data.

6. What is the difference between SPX GEX and SPY GEX?
SPX GEX is based on index options, while SPY GEX reflects ETF options positioning. Liquidity and contract structure differ.

7. Can GEX flip during the day?
Yes. Large price moves or expiration-related positioning changes can cause gamma exposure to shift.

Unlocking Market Insights with the SIV Index

While this curve uses simplified positioning assumptions, it can offer some limited, but key insights. Monitoring the daily changes to this curve can offer insights into how traders are adjusting their options positions.

For improved forecasting power, SpotGamma subscribers have access to the SpotGamma Implied Volatility (SIV) Index, an improved method to forecast market volatility. This metric is derived from studies into the interaction between measurements of S&P 500 Gamma, changes in implied volatility and movement in the S&P 500.