Press note
Polymarket and Kalshi Order Book Depth: 10,000 Contracts Fit 64% and 57% of Books
64%Polymarket books that could fill 10,000 contracts
1,717 of 2,701 books, 17–18 September 2026; 78% could fill 1,000 and all could fill 100
Vultax walked the displayed asks in 10,282 order-book snapshots at three order sizes. 100 contracts fit almost every book. 10,000 fit 64% of Polymarket books at a median 0.25¢ above the best ask, and 57% of Kalshi books at 15.38¢ above it. The quoted price holds for 100 contracts and often not for 10,000. Every one of 2,701 Polymarket order books showed enough asks to fill 100 contracts, 78% showed enough for 1,000, and 64% enough for 10,000. On Kalshi the shares were 99.9%, 96% and 57% of 1,188 books. Where the order did fit, it cost little on Polymarket and a lot on Kalshi. The two venues were sampled on different watchlists, so each venue's figures stand on their own.
Observed 2026-09-17 to 2026-09-18, population: 2,701 Polymarket order-book snapshots with a positive, uncrossed bid and a best ask between 10¢ and 90¢.
Supporting figures
- 57% — Kalshi books that could fill 10,000 contracts680 of 1,188 books; 96% could fill 1,000 and all but one could fill 100
- 0.25¢ vs 15.38¢ — Median cost above the best ask at 10,000 contractsPolymarket vs Kalshi, per contract, among books that could fill the order; before fees
- 10,282 — Order books walkedFirst snapshot of each UTC hour over 48 hours: 7,354 Polymarket, 2,928 Kalshi
Images
Vultax Research
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Links
- The study
- Full text, sources and method
- Markdown edition
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- Chart figures (CSV)
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- All datasets (JSON)
- Every published table and chart, with units and sources
- Open the Polymarket market directory
- Every open Polymarket market with its Yes price, 24-hour volume and resting liquidity: check the book before sizing an order.
Press contact
Vultax Research — [email protected]
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How to cite
Vultax Research, Polymarket and Kalshi Order Book Depth: 10,000 Contracts Fit 64% and 57% of Books, 2026-09-20, https://vultax.com/research/prediction-market-order-size-depth-audit
Published 2026-09-20. Figures are the published study; live screens move. Plain-text version · Use our data