Open interest counts outstanding contracts in a particular option series. Each contract has a long and a short side but is counted once. A trade adds one contract when both sides open, removes one when both sides close, and leaves the count unchanged when one side opens and the other closes. Exercise and expiration can also reduce the count.
Open interest indicates participation, but does not guarantee liquidity or an easy large-order fill. Check current bid/ask prices, displayed size and quote time. A processed open-interest total is different from today’s trading volume.
Research open interest
Explore open interest on Market Chameleon alongside your own analysis.
Full screening features may require a paid subscription. Market data is delayed.
How opening and closing trades change the count
| Buyer | Seller | Open-interest change |
|---|---|---|
| Opens a long | Opens a short | +1 |
| Closes a short | Closes a long | −1 |
| Opens a long | Closes a long | 0 |
| Closes a short | Opens a short | 0 |
If starting open interest is 1,000 and trades create 40 new pairs, close 25 pairs and transfer 60 existing contracts, volume from those transactions is 125 contracts while open interest becomes 1,015, ignoring exercises and other changes. Volume counts activity; open interest counts the contracts that remain.
Published open interest usually reflects a processed snapshot rather than a live tally of every intraday trade. Check the data timestamp. It cannot identify whether the long is a customer, dealer, hedger or speculator, and a high count does not guarantee a narrow spread in your required quantity.
