Does 1,000 contracts of OI establish dealer Gamma's sign?
Reveal the worked answer
No.
Ownership and offsetting positions must be known or explicitly modeled.
Dealer Logic · DL-06 · Core
Strike concentration and pinning
Why does large open interest not guarantee a pin?
What you will learn and prerequisites
- Explain the mechanism in the lesson question.
- Reproduce the worked comparison and recognize its failure case.
Read first: Why dealers hedge
A large option concentration can make a strike relevant to hedging, particularly near expiration. It does not force settlement at that strike. Open interest counts contracts, each with a long and a short, but does not by itself establish dealer ownership.
Understand the mechanism
At-the-money Gamma can concentrate as expiry approaches, while far-away options behave differently. A positively signed, actively hedged inventory may generate opposing flow around a strike; a negatively signed inventory may amplify movement.
Other expiries, settlement mechanics and external orders can outweigh that channel. A concentration is a research location, not a guaranteed magnet.
Walk through the process
Identify the exact product, expiry and sensitivity measure. Separate unsigned OI from signed exposure and compare possible hedge size with available liquidity.
Keep a move-away branch in the plan. Holding a short option into expiry solely because of a presumed pin leaves assignment and gap risk unresolved.
Evidence boundary
The arithmetic is original conditional teaching material, not a measurement of current dealer positions. The cited Cboe research is historical product-specific evidence, not a live inventory feed. Model outputs should remain distinguishable from observed market facts.
A worked example
A fictional strike has 1,000 calls open and per-unit Gamma 0.04. With a 100 multiplier, the magnitude is 4,000 shares per dollar. A dealer long all of them has +4,000; a dealer short all has −4,000.
The same unsigned OI supports opposite possible hedge directions. The chart makes that missing sign explicit rather than inferring it.
Strike concentration and pinning—worked comparison
Vertical: Gamma (shares/USD)
Horizontal: Ownership assumption
1. Fictional example
Read the graph as a data table
| Ownership assumption | Fictional example |
|---|---|
| 1 | 4,000 |
| 2 | -4,000 |
What would invalidate the reading?
Assuming that all open calls are dealer-long calls can invert the entire explanation. Strong external flow can also overwhelm genuine pinning feedback.
Check your understanding
Try the question before revealing its answer. These are reading checks, not trading certification or a site completion record.
What is the critical failure to avoid?
Reveal the worked answer
Assuming that all open calls are dealer-long calls can invert the entire explanation. Strong external flow can also overwhelm genuine pinning feedback.
Explain this risk before treating the example as a decision rule. A correct calculation does not guarantee a favorable market outcome.
Return to the question: Why does large open interest not guarantee a pin? State the observed facts, the assumptions and the failure condition separately.
Sources, assumptions and downloadable script
External references support definitions and conventions. Worked scenarios and prose are original. No current quotes or dealer inventory are claimed.
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