What is open interest?

Open interest versus volume

These two numbers are constantly confused, and they answer different questions. Volume asks how much changed hands during a period. Open interest asks how much is currently at stake.

A single contract traded back and forth between two traders ten times produces ten units of volume and leaves open interest unchanged. A single contract opened once and held produces one unit of volume and adds one unit of open interest that persists until the position closes.

This is why a venue can show enormous volume with modest open interest — that pattern indicates short-term flow rather than held exposure — while another shows the reverse.

How open interest changes

Every perpetual position has a trader on each side. Open interest changes only when the total number of open contracts changes, which depends on whether the two parties to a trade are opening or closing.

Both opening

A new buyer meets a new seller. A contract that did not exist before now does, and open interest rises.

Both closing

An existing long sells to an existing short who is buying back. The contract is extinguished and open interest falls.

One opening, one closing

A position simply transfers from one trader to another. Volume is generated, open interest is unchanged.

Reading it alongside price

Open interest on its own says nothing about direction — it counts contracts, not sentiment. It becomes informative when read with price.

Price rising with open interest rising means new money is entering long. Price rising with open interest falling usually means shorts are covering, which is a weaker signal because the buying is forced rather than fresh conviction. Price falling with open interest rising means new shorts are being opened, while price falling with open interest falling is long liquidation or profit-taking.

None of these are trading signals in isolation. They are descriptions of what kind of flow is behind a move, which is more useful than the move alone.

Why high open interest raises liquidation risk

Large open interest means large leveraged exposure sitting on the books. When price moves against a crowded side, positions get liquidated, and liquidations are forced market orders that push price further in the same direction — which liquidates more positions.

That is the mechanism behind cascade moves. Open interest does not cause them, but it measures how much fuel is available if one starts. Reading open interest with funding gives a fuller picture: heavy open interest plus heavy positive funding means a large, crowded, expensive long side.

Comparing open interest between venues

Open interest is usually quoted in notional dollar terms, which makes it comparable across venues in principle. In practice, venues differ in what they include — some report per-market, some aggregate, and definitions of notional can vary with how the index price is computed.

Treat cross-venue open interest as approximate. The trend on a single venue over time is more reliable than a precise ranking between venues at one moment.