On July 18, 2026, VolRoc recorded 215,570 active prediction markets across Kalshi and Polymarket, holding $1.91B in combined open interest. Day over day, active markets rose 59.4% and open interest rose 18.7% (vs July 17, 2026). Sports was the largest domain by open interest (47%), ahead of Politics & Elections (24%); together they accounted for 70% of all open interest. Kalshi carried 83% of active markets and Polymarket 17%.
Deterministic · template v1 · 2026-07-18
As of 2026-07-18 · 00:00 UTC
Active Markets
215,570
00:00 UTC freeze
Open Interest
$1.91B
Kalshi OI + Polymarket liquidity
Markets Traded · 24h
20,967
with trading activity
Kalshi / Polymarket
83% / 17%
by active-market count
Domain Composition — 12 domains
Sports
149,888
Other
25,651
Mixed / Multi-category
24,621
Politics & Elections
6,423
Entertainment & Culture
2,606
Crypto & Digital Assets
1,757
Climate & Weather
1,189
Companies & Business
955
Economics & Inflation
816
Technology & AI
653
World & Geopolitics
489
Monetary Policy
436
Science & Health
86
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 = 215,570.
Largest Kalshi Series
Sports — multi-game parlays
125,665
Cross-category multi-markets
24,621
Midterm control
866
Music — artist streams
774
U.S. House races
593
Nextteamnba
441
NFL — next team moves
254
Nextteammlb
221
Nflwins
209
Pgatour
205
Wcaward
201
Mlbhr
196
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 18, 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 18, 2026.” https://volroc.ai/prediction-markets/2026-07-18/
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