Volume vs Open Interest
Definition
Volume is the number of contracts traded during a period; the CFTC defines it as 'the number of contracts traded during a specified period of time.' Open interest is the number of contracts entered into and not yet closed out or settled; the CFTC calls it the total 'not yet liquidated by an offsetting transaction or fulfilled by delivery.' Neither measures how much can be traded now at a good price, which is depth.
Why it matters
Volume headlines describe a venue, not a contract. Investors should check a specific market's open interest, recent volume and current book before assuming they can trade or exit in size, and treat aggregate volume figures as marketing context rather than a measure of liquidity.
Common misconceptions
- •Volume is not liquidity.
- •High open interest is not an exit; it can mean many holders competing to sell.
- •Venue-wide volume is concentrated in a few series; most contracts trade little or not at all.
- •The label is only a starting point. Investor outcomes usually depend on the governing documents, cash-flow priority, valuation policy, disclosure quality, and manager discretion surrounding the term, not just the shorthand definition used in marketing materials.
Technical details
Worked example (illustrative)
Market A: two traders flip 100 contracts 20 times; volume 2,000, open interest 100.
Market B: one buyer holds 1,500 contracts bought from several sellers; volume 1,500, open interest 1,500.
Market A looks busier, but Market B carries fifteen times the outstanding exposure.
How investors apply the term
Investors usually apply this term by tying the definition back to the controlling documents and then asking which cash flows, rights, restrictions, or valuation assumptions it changes. A useful review looks at the term alongside fees, leverage, liquidity, reporting frequency, and manager discretion rather than treating it as a standalone concept.
The practical diligence test is simple: identify who benefits if the assumption is wrong, who has control when conditions change, and what evidence the investor receives after closing. Terms that cannot be reconciled to documents, cash movements, and monitoring data should be treated as marketing shorthand until proven otherwise.
Frequently asked questions
- Does high trading volume mean a prediction market is deep?
- No. Volume can come from a few traders turning over the same small position. Two traders passing 100 contracts back and forth 20 times create 2,000 contracts of volume but only 100 of open interest; one trader buying and holding 1,500 creates 1,500 of each. Neither tells you what is resting in the book now.
- What does open interest tell me?
- How much exposure is outstanding, and so how much money depends on the resolution. A market with high open interest and a thin book can be hard to exit, because holders who want out compete for few bids.
- How concentrated is volume?
- Very, on AltStreet's Kalshi data. The single largest series accounted for 58.6% of recorded volume and the top three for 81.3%. In a frame of 82,006 open contracts, 89.4% had recorded zero volume and 92.0% less than 100 contracts.