About $7 trillion in U.S. options notional value is scheduled to expire on Friday, creating one of the largest options-expiry events on record and potentially altering market dynamics, according to Citadel Securities.

The expiration, known as “triple witching,” brings together the expiry of monthly S&P 500 index options and options on individual stocks. Citadel Securities estimates that the event will rank as the second-largest on record, with the expiring positions representing roughly one-quarter of the U.S. market.

The size of the expiry could have implications for trading conditions as investors and market makers adjust or roll their positions. Around 60% of the contracts are expected to expire at the market open, Citadel Securities said.

The firm’s market intelligence team, led by Scott Rubner, said the event could mark a significant change in the market’s technical setup.

Large options positions have recently helped limit the magnitude of market moves in some circumstances. As those positions expire or are rolled into new contracts, however, that effect could weaken, potentially leaving stocks more exposed to incoming buying and selling pressure.

“Triple witching” occurs four times a year, when several major classes of equity derivatives expire simultaneously. Such events can lead to elevated trading volumes and changes in market positioning as investors close, exercise or replace expiring contracts.

For Friday’s session, the unusually large scale of the expiration means traders will be watching closely for any shifts in volatility and market sensitivity once the expiring positions are cleared.