What Open Interest Measures
Open interest (OI) is the total number of outstanding option contracts that have not been settled or closed. It updates once per day, after the previous session closes — so what you see in the morning reflects yesterday's closing position.
Rising OI means new positions are being opened — money flowing in, commitment increasing. Falling OI means positions are being closed or expiring — the trade is coming off, conviction is declining. OI is a measure of commitment: it shows you where money is parked over time, not just what happened today.
A strike with 50,000 OI has deep, established interest. A strike with 200 OI is lightly held — and any volume spike there will look enormous in percentage terms but may represent just a handful of traders.
What Volume Measures
Volume is the number of contracts traded on the current day. It resets to zero at market open. High volume means a lot of activity happened today — but without OI context, you don't know if it's opening new positions, closing existing ones, or both.
Volume alone answers: "Was there activity?" OI answers: "Is there commitment?" The real signal comes from combining them.
| Metric | Resets | What it tracks | Best used for |
|---|---|---|---|
| Volume | Daily | Today's trading activity | Spotting today's unusual activity |
| Open Interest | Daily (prior session) | Outstanding contracts | Measuring commitment over time |
| Vol/OI Ratio | Calculated | Activity vs base | Flagging unusual activity |
The Vol/OI Ratio: Why It Signals Unusual Activity
The Vol/OI ratio = today's volume ÷ yesterday's OI. This normalization is what makes it powerful.
Consider two scenarios: (1) A strike with 10,000 OI sees 2,000 contracts trade — a Vol/OI of 0.2, totally unremarkable. (2) A strike with 400 OI sees 2,000 contracts trade — a Vol/OI of 5, meaning 5× the existing position traded in a single day. The raw volume number (2,000) looks identical. The Vol/OI ratio reveals they're completely different situations.
Ratio of 1.0 → trading equaled the existing position (already unusual)
Ratio of 5.0 → 5× the existing position traded today (highly unusual)
Ratio of 10.0 → 10× the existing position (extremely abnormal)
The ratio normalizes volume by the baseline of existing interest, making it directly comparable across different strikes, tickers, and market caps. A ratio of 5× on AAPL is equally significant as a ratio of 5× on a mid-cap stock.
How Greeks Classifies Signals
The Greeks unusual flow screener uses the Vol/OI ratio to classify signals automatically. The thresholds are calibrated to surface genuinely abnormal activity while filtering out routine daily noise:
| Vol/OI Ratio | Signal | Severity | Interpretation |
|---|---|---|---|
| ≥ 8× | Unusual Volume | High | Extremely abnormal — large directional bet or news-driven activity |
| 3× – 8× | Unusual Volume | Medium | Significant above-average — monitor for follow-through |
| OI = 0, Vol ≥ 50 | Opening Position | Medium | Brand new position — fresh conviction with no prior OI |
Reading Conviction: Strike, DTE, Call vs Put
The Vol/OI ratio identifies that something unusual happened. The context around it tells you whether it represents high-conviction directional positioning:
- Strike distance from spot: OTM options signal more speculative or directional positioning — someone believes price will move significantly. ATM or near-ATM options could be hedging existing equity exposure.
- DTE: Short DTE (less than 14 days) combined with high Vol/OI = high urgency. This trader expects the move to happen quickly. Longer DTE gives more time for the thesis to play out but requires more premium — suggesting higher conviction in the direction, not necessarily the timing.
- Call vs Put: In isolation, call buying does not equal bullish (it could be a hedge against a short equity position). Put buying does not equal bearish (it could be portfolio protection). Look for sweeps — multiple fills across multiple strikes in the same direction within a short window — as the strongest directional signal.
Rising OI + rising price = bullish confirmation. Rising OI + falling price = bearish confirmation. Falling OI in either direction = positions are closing — the move may be ending. Use OI change day-over-day alongside price action to distinguish new positioning from position unwinding.
Example Scenarios
Here's how to apply this framework to real situations you'll encounter in the flow screener:
Large OTM Call Sweep
10,000 contracts of a 30-delta call, DTE = 7, Vol/OI = 12×, new position (prior OI was only 800). This is a high-conviction bullish signal. The short DTE means the trader expects the move within a week. The OTM strike means they're looking for a significant move, not a grind. The 12× ratio signals someone paid up for urgent exposure. This warrants close monitoring for follow-through in the underlying.
Put Wall Buildup
OI grows by 20,000 contracts at a round number put strike over 3 consecutive sessions, and price is approaching from above. This is a different signal: dealers are accumulating short gamma at this strike. To hedge, they must sell the underlying as price approaches — which creates mechanical support. This "put wall" is visible as a red bar on the GEX by Strike chart and represents a structural level, not a directional bet.
Same-day expiry (0DTE) flow with high Vol/OI is often gamma scalping by market makers or day traders, not directional institutional positioning. 0DTE contracts reset to zero gamma at close — so large volume ratios are common and carry less informational signal than equivalent ratios on longer-dated contracts. Weight 0DTE flow differently from 7+ DTE flow.