Definition · updated 2026-10-21
OPEX (options expiration)
OPEX is options expiration, most often the monthly expiration on the third Friday when the largest block of open interest settles. Because dealer hedges tied to those contracts are unwound at once, the sessions around OPEX often pin to heavy strikes, and the week after frequently breaks the range.
See it live: today's GEX levels by ticker.
Why OPEX changes the tape
Gamma exposure is highest into expiration and vanishes at the close. Pinning near the biggest strikes is common on the day; the removal of that gamma afterwards leaves the market freer to trend, which is why large moves cluster in the following week.
Quarterly expirations (March, June, September, December) also settle index futures and many structured products, which is why they are called triple or quad witching.
Frequently asked questions
- What does OPEX mean in trading?
- The day options expire, usually the third Friday of the month for monthly contracts.
- Why does the market move after OPEX?
- The dealer gamma that pinned price into expiration is gone, so hedging no longer dampens moves and trends develop more easily.