TL;DRThe total number of outstanding (open) futures contracts at any given time. Rising open interest means new money is entering the market. Falling open interest means positions are being closed.
Open interest counts the total number of futures contracts that are currently open (held by traders). Every futures trade has a buyer and a seller, so one contract of open interest represents one long position and one short position.
Open interest increases when a new buyer and a new seller both open positions (creating a new contract). It decreases when an existing buyer and an existing seller both close their positions (extinguishing a contract). It stays the same when one side is opening and the other is closing.
The relationship between open interest changes and price movement reveals who is driving the market.
Rising price with rising OI: new longs are entering. This is the most bullish combination because new money is backing the uptrend.
Rising price with falling OI: shorts are covering (closing). The rally is driven by short-covering, not new buying. This often produces less sustainable moves.
Falling price with rising OI: new shorts are entering. Bearish conviction is increasing.
Falling price with falling OI: longs are exiting. The decline is driven by liquidation, not new selling.
Open interest is most useful as a confirmation tool, not a primary signal. If you see a breakout above resistance and open interest is increasing, the breakout has more credibility because new participants are committing capital.
Watch OI during the approach to expiration. Falling OI near expiration is normal (traders rolling to the next month). But if OI drops sharply outside of the roll period, it suggests traders are exiting, which can reduce liquidity.
Extreme open interest readings (historically high or low) can signal inflection points. When everyone who wants to be positioned already is (high OI), there's less fuel for continued moves. When OI is very low, a catalyst can cause a sharp move as new participants rush in.
New longs entering a trend
ES breaks above a multi-week resistance level at 5,250. Open interest increases by 50,000 contracts over the next three days.
Rising price with rising OI confirms that new buyers are entering. This is stronger than a breakout on declining OI (which would suggest the move is driven by short-covering). The uptrend has new money behind it.
Short covering rally
ES drops from 5,200 to 5,100 over two weeks. Open interest rose during the decline (shorts entering). Now ES bounces to 5,140 and OI drops by 30,000.
The bounce is short-covering (shorts closing profitable positions), not new buying. This rally may be temporary. Once the short-covering is done, selling could resume if no new buyers step in.
Confusing open interest with volume
Volume counts the number of contracts traded during a period. OI counts contracts still open. High volume can occur with no change in OI (if the same number of contracts are being opened and closed).
Ignoring open interest during rollover periods
OI drops in the expiring contract and rises in the next month during rollover. This is mechanical, not directional. Adjust your analysis during roll weeks.
Using daily OI changes as a trading signal without price context
OI change alone doesn't tell you direction. You need to combine it with price action to understand whether new longs, new shorts, or position closures are driving the change.