On September 16, 2026, VolRoc recorded 318,384 active prediction markets across Kalshi and Polymarket, holding $2.11B in combined open interest. Day over day, active markets fell 1.6% and open interest rose 3.8% (vs September 15, 2026). Politics & Elections was the largest domain by open interest (27%), ahead of Sports (18%); together they accounted for 45% of all open interest. Kalshi carried 85% of active markets and Polymarket 15%.
Deterministic · template v1 · 2026-09-16
As of 2026-09-16 · 00:00 UTC
Active Markets
318,384
00:00 UTC freeze
Open Interest
$2.11B
Kalshi OI + Polymarket liquidity
Markets Traded · 24h
25,458
with trading activity
Kalshi / Polymarket
85% / 15%
by active-market count
Domain Composition — 12 domains
Mixed / Multi-category
231,106
Sports
35,032
Other
32,117
Politics & Elections
10,517
Entertainment & Culture
3,068
Crypto & Digital Assets
1,670
Technology & AI
1,386
Economics & Inflation
925
World & Geopolitics
830
Companies & Business
794
Monetary Policy
547
Climate & Weather
278
Science & Health
114
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 = 318,384.
Largest Kalshi Series
Cross-category multi-markets
208,585
KXMVECROSSCATEGORY0
22,521
Midterm control
1,360
Votegeneral
1,156
Music — artist streams
698
U.S. House races
649
Ncaafspread
490
Ncaafwins
431
Nextteamnba
424
Nflwins
399
Ncaaftotal
349
Mlbhr
324
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 September 16, 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 — September 16, 2026.” https://volroc.ai/prediction-markets/2026-09-16/
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