#Definition
Open interest is the total number of outstanding contracts held by market participants at any given time. In prediction markets, it represents the sum of all Yes shares held (or equivalently, all No shares held, since each Yes has a corresponding No).
Unlike trading volume, which measures activity, open interest measures commitment: how many positions currently exist that will need to settle at resolution. High open interest indicates significant capital committed to the market's outcome.
#Why It Matters in Prediction Markets
Open interest reveals important information about market health and trader behavior:
Market significance
Higher open interest suggests more traders care about the outcome. A market with 10,000.
Liquidity proxy
Open interest correlates with available liquidity. Markets with high open interest typically have tighter spreads and less slippage because more participants are available to trade.
Settlement obligations
Open interest determines how much money changes hands at resolution. A market with 100,000 shares open will settle 1 per winning share).
Conviction indicator
Rising open interest alongside rising prices suggests new money entering long positions (genuine conviction). Rising prices with flat open interest might just be position shuffling between existing participants.
#How It Works
#Open Interest Mechanics
In prediction markets with Yes/No share pairs:
Open Interest = Total Yes shares outstanding = Total No shares outstanding
These are equal because every Yes share has a corresponding No share; they're created together when collateral is deposited.
#How Open Interest Changes
Open interest increases when:
- New trader deposits collateral and receives Yes + No shares
- New trader buys from an AMM that mints new shares
Open interest decreases when:
- Trader redeems complete set (Yes + No) for collateral
- Market resolves and shares are settled
Open interest stays same when:
- Existing shares change hands between traders
- Price changes without new position creation
#Numerical Example
Day 1: Market opens
- Alice deposits $100, receives 100 Yes + 100 No
- Bob deposits $200, receives 200 Yes + 200 No
- Open interest: 300 shares
Day 2: Trading occurs
- Alice sells her 100 Yes to Carol for $60
- Open interest: Still 300 shares (shares changed hands, no net change)
Day 3: New entry
- Dave deposits $150, receives 150 Yes + 150 No
- Open interest: 450 shares
Day 4: Exit
- Bob redeems 100 Yes + 100 No for $100 collateral
- Open interest: 350 shares
Resolution: Market resolves Yes
- 350 Yes shares pay 350 to Yes holders
- 350 No shares pay 0 to No holders
- Open interest: 0 (market closed)
#Open Interest vs. Volume
| Metric | What It Measures | Interpretation |
|---|---|---|
| Open Interest | Outstanding positions | Commitment to outcome |
| Volume | Trades executed | Activity level |
A market can have high volume but low open interest if the same positions trade back and forth. High open interest with low volume suggests committed holders not actively trading.
#Visualizing Divergence
Line = Open Interest (Steady growth), Bar = Volume (Spiky activity)
#Examples
#Example 1: Conviction Signal
Election market over time:
| Date | Price | Open Interest | Volume | Interpretation |
|---|---|---|---|---|
| Jan 1 | $0.40 | 50,000 | 5,000 | Base state |
| Feb 1 | $0.55 | 80,000 | 15,000 | New money entering long |
| Mar 1 | $0.55 | 80,000 | 20,000 | Churning, no new commitment |
| Apr 1 | $0.60 | 100,000 | 25,000 | Strong conviction, price + OI rising |
The April state shows genuine momentum: both price and open interest increasing.
#Example 2: Shorts Building
A market on a company hitting earnings:
| Date | Price | Open Interest | Interpretation |
|---|---|---|---|
| Week 1 | $0.75 | 20,000 | Initial state |
| Week 2 | $0.70 | 35,000 | Price down, OI up = short interest building |
| Week 3 | $0.72 | 35,000 | Slight recovery, shorts not covering |
Rising open interest while price falls suggests new short positions, not just existing longs selling.
#Example 3: Resolution Approaching
As resolution nears, behavior changes:
| Time to Resolution | Open Interest | Behavior |
|---|---|---|
| 30 days | 100,000 | Normal trading |
| 7 days | 95,000 | Some early exits |
| 1 day | 85,000 | Profit-taking, uncertainty reduction |
| Resolution | 0 | All positions settled |
#Example 4: Comparing Market Significance
Two markets on election day:
- Presidential race: $15 million open interest
- Local ballot measure: $50,000 open interest
The presidential market's price is more trustworthy; more capital is committed to getting it right.
#Risks, Pitfalls, and Misunderstandings
Confusing open interest with liquidity
High open interest doesn't guarantee good execution. If holders aren't actively trading, the order book might still be thin. Check active bids/asks, not just outstanding shares.
Ignoring open interest distribution
Total open interest doesn't tell you who holds it. A market with 100,000 shares might have 1,000 traders with 100 each, or 10 traders with 10,000 each. The latter is more fragile.
Misreading OI changes
Open interest falling during price rises could mean profit-taking (bullish holders selling to new entrants) or shorts covering (previous bears exiting). Context matters.
Resolution mechanics
At resolution, open interest doesn't "go" anywhere; winning shares pay 0. The "interest" is settled, not transferred.
#Practical Tips
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Use open interest to gauge market credibility: Higher OI markets deserve more trust in their price signals
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Watch OI trends with price: Rising price + rising OI = strong conviction. Rising price + flat OI = weaker signal
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Consider your impact: In low OI markets, your trades more significantly affect the market. Size accordingly
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Monitor OI for crowding: If OI is highly concentrated on one side at extreme prices, there may be squeeze potential
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Factor OI into liquidity assessment: High OI typically means easier exits, but verify by checking actual order book depth
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Track OI over time: Sudden OI changes can signal informed positioning or approaching events
#Related Terms
#FAQ
#How is open interest different from market cap?
Open interest is the number of shares/contracts outstanding. "Market cap" in prediction markets would be open interest times share price for one side. A market with 100,000 shares at 60,000 in Yes-side "market cap" but 100,000 open interest.
#Can open interest decrease while price increases?
Yes. If existing holders sell to each other (no net change) while some holders redeem complete sets (reducing OI), the price can rise on lower volume while OI falls. This might indicate profit-taking by early longs.
#What's a "good" level of open interest?
It depends on the market and your trade size. For personal trading, you want OI high enough that your orders don't significantly move the market. For trusting price signals, higher OI generally means more reliable information aggregation.
#Do AMM-based markets have open interest?
Yes, but it's calculated differently. In AMM pools, open interest represents tokens in circulation outside the pool. When the pool mints new tokens to satisfy trades, open interest increases. The concept applies but the mechanics differ from order book markets.
#Why does open interest matter at resolution?
Open interest determines settlement amounts. If a market has 500,000 shares open and resolves Yes, $500,000 flows to Yes holders. Platforms and traders need to know OI to understand the financial stakes involved.