Dealer Gamma, Delta Hedging, and Price Behavior Near Options Expiry
Summary
The document distinguishes put-call gamma imbalance from a mismatch between the gamma of a put and a call at the same strike, noting that put-call parity remains intact. It discusses how dealers’ or traders’ hedging behavior may affect the underlying market as options approach expiration. In its example, holders of a near-the-money straddle hedge by buying stock as it falls and selling as it rises, which may create pressure around the strike.
The explanation also describes a possible change in behavior after a substantial market move: short option holders may need to adjust delta exposure more forcefully, adding to price movement. The account is qualitative and based on an illustrative scenario rather than empirical analysis. It does not define how to measure aggregate gamma positioning, and its pinning and volatility effects are conditional, not guaranteed outcomes.
Key ideas
- Put-call gamma imbalance does not mean that a put and call at the same strike have unequal gamma.
- The answer describes how long straddle holders may hedge by buying on declines and selling on rallies.
- This hedging pattern may contribute to price pinning near a strike as expiration approaches.
- A large underlying move may prompt short option holders to hedge more urgently and intensify volatility.
- The explanation is qualitative and does not measure market-wide positioning.
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Full text
# Gamma Imbalance Explanation # Gamma Imbalance Explanation Can someone please give me an explanation as to what put-call gamma imbalance specifically refers to (imbalance of what?), and why they may exacerbate volatility from a market perspective, and why the risk increases on option expiry day? My guess is it that these imbalances force option sellers/dealers to more aggressively delta-hedge their positions, but I would like to have a better grasp on what is really going on. Some confustion is coming from the fact that I thought put and call gamma must be equal else put/call parity would be violated based on put delta + call delta = 1 for a given option strike. ## Answer by John (score 0, accepted) https://quant.stackexchange.com/a/20632 I do not think the term put-call gamma imbalance refers to the imbalance between "a put" and "a call" at the same strike. . .so put call parity lives on. As for the exacerbated volatility, my experience has shown that there is pressure to "pin" at a strike which would decrease volatility near expiry. scenario: ``` Strike = 100 Stock =100 expiry in 10 minutes all else equal ``` Those traders long the 100 straddle will scalp their gamma aggressively in the final moments. As the stock trades below 100, the 100 straddle will generate short stock for the long holder. The long option holder buys stock as it drops and sells it as it rallies butting pressure on the stock to stay at 100. The short option holder locks in losses every time he hedges so is more incline to not take such energetic hedging action as that of the longs. Now, if the market makes a surprise move of substance. . .all bets are off, there may exist a very large delta imbalance (short option holders) and they might be forced (pain of large loses changes everything) to sell their long deltas on the downside or buy in their short delta on the upside. In either case this will increase volatility . . .until the next trike is reached and the "pinning" battle can begin again. this article gives a better explanation than mine :-) http://realmoney.thestreet.com/articles/12/15/2011/how-options-expiration-affects-stock-prices
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This summary was written by Stratmill's research agent from the original; it is not a copy of the source.