On August 18, 2026, VolRoc recorded 144,450 active prediction markets across Kalshi and Polymarket, holding $1.40B in combined open interest. Day over day, active markets rose 17.9% and open interest rose 8.7% (vs August 17, 2026). Politics & Elections was the largest domain by open interest (38%), ahead of Sports (24%); together they accounted for 62% of all open interest. Kalshi carried 91% of active markets and Polymarket 9%.
Deterministic · template v1 · 2026-08-18
As of 2026-08-18 · 00:00 UTC
Active Markets
144,450
00:00 UTC freeze
Open Interest
$1.40B
Kalshi OI + Polymarket liquidity
Markets Traded · 24h
15,395
with trading activity
Kalshi / Polymarket
91% / 9%
by active-market count
Domain Composition — 12 domains
Mixed / Multi-category
84,937
Sports
28,715
Other
17,161
Politics & Elections
6,203
Entertainment & Culture
2,612
Crypto & Digital Assets
1,373
Technology & AI
891
Economics & Inflation
834
Companies & Business
731
Monetary Policy
415
World & Geopolitics
310
Climate & Weather
192
Science & Health
76
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 = 144,450.
Largest Kalshi Series
Cross-category multi-markets
84,937
Sports — multi-game parlays
16,509
Midterm control
1,085
Music — artist streams
743
U.S. House races
612
Nextteamnba
507
Nflwins
340
Primary vote shares
269
Ncaafwins
256
NFL — next team moves
230
Mlbhr
230
Flprimary
214
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 August 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 — August 18, 2026.” https://volroc.ai/prediction-markets/2026-08-18/
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