On July 31, 2026, VolRoc recorded 148,408 active prediction markets across Kalshi and Polymarket, holding $1.46B in combined open interest. Day over day, active markets rose 3.7% and open interest rose 8.2% (vs July 30, 2026). Sports was the largest domain by open interest (41%), ahead of Politics & Elections (33%); together they accounted for 75% of all open interest. Kalshi carried 80% of active markets and Polymarket 20%.
Deterministic · template v1 · 2026-07-31
As of 2026-07-31 · 00:00 UTC
Active Markets
148,408
00:00 UTC freeze
Open Interest
$1.46B
Kalshi OI + Polymarket liquidity
Markets Traded · 24h
17,582
with trading activity
Kalshi / Polymarket
80% / 20%
by active-market count
Domain Composition — 12 domains
Sports
94,719
Other
23,055
Mixed / Multi-category
15,736
Politics & Elections
6,583
Entertainment & Culture
2,657
Crypto & Digital Assets
1,454
Companies & Business
1,125
Technology & AI
1,059
Economics & Inflation
952
World & Geopolitics
396
Monetary Policy
365
Climate & Weather
214
Science & Health
93
Venue-agnostic subject taxonomy from Kalshi series prefixes and
Polymarket title keywords. A residual Other bucket is reported honestly.
Yes-price across both venues, 10 buckets from 0 to 100. n = 148,408.
Largest Kalshi Series
Sports — multi-game parlays
74,642
Cross-category multi-markets
15,736
Midterm control
948
Music — artist streams
757
U.S. House races
601
Nextteamnba
482
Nflwins
263
NFL — next team moves
257
Nextteammlb
238
Flprimary
203
Rt
166
Midtermvoteturn
163
Kalshi market families (Polymarket is not series-structured).
About & Citation
This is the fixed-hour (00:00 UTC) state of every active market on
Kalshi and Polymarket for July 31, 2026. The live
Observatory
shows the current diurnal value; this record is immutable. Open interest combines Kalshi
open interest with Polymarket USD liquidity as comparable USD magnitudes. Sources: Kalshi, Polymarket.
How to cite
“VolRoc Prediction Market Archive — July 31, 2026.” https://volroc.ai/prediction-markets/2026-07-31/
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