Glossary

What Is Open Interest (OI) in Options?

Open interest (OI) counts option contracts that are open — not yet closed or expired. It is a positioning stock, while volume is a flow of trades over a period.

Unique context: OptionData option-chain REST responses include open interest with bid/ask, volume, IV, and Greeks so unusual-activity rules can compare print size to standing OI — not just raw premium.

Option chain API UOA workflow

How OI is used with flow

Pair chain OI with live prints to judge whether activity is large relative to existing positioning.

Fetch chain OI

Pull the option chain for a symbol to read OI by strike and expiry before or after an alert.

Compare size to OI

A print that is large versus OI may matter more than the same premium on a deep, liquid contract.

Track OI changes over days

Day-over-day OI shifts (from successive chain snapshots) inform positioning studies.

Do not confuse with volume

Volume resets with the session’s trades; OI persists until contracts close or expire.

OI vs volume vs flow

Open interest — open contracts outstanding
Volume — contracts traded in a window
Options flow — sequence of individual prints
UOA rules often combine premium + OI + DTE
OptionData: OI on chain API; flow on WebSocket
Historical SQL for trade prints; chains for OI snapshots

Example: request chain including OI context

// Chain snapshot fields typically include open interest per contract
// Use OI with live premium to gauge size-vs-positioning context.
await fetch('https://www.optiondata.io/api/option-chain', {
  method: 'POST',
  headers: { Authorization: 'Bearer KEY', 'Content-Type': 'application/json' },
  body: JSON.stringify({ symbol: 'TSLA' }),
});

Related terms and workflows

OI is most useful next to flow and UOA pages.

Open interest FAQ