One 2025 study estimates that wash-trading-like patterns accounted for nearly a quarter of Polymarket’s historical trading volume, but it does not prove that every flagged trade was fraudulent. Its estimates changed sharply over time, while a separate 2026 study found a much lower rate in a narrower set of markets using a different measure. The findings are not directly comparable.
What the 2025 study says about Polymarket
In Network-Based Detection of Wash Trading, dated November 6, 2025, Allen Sirolly, Hongyao Ma, Yash Kanoria, and Rajiv Sethi estimate that nearly 25% of Polymarket’s historical volume showed patterns their algorithm classified as likely wash trading. The study examined trades from November 21, 2022, through October 12, 2025, and flagged 14% of the 1.26 million wallets that had traded on the platform.
The estimated share varied substantially across time and market categories. These are the authors’ algorithm-based estimates, not verified rates of fraud:
| Measure | Estimate reported by the 2025 study |
|---|---|
| Historical volume, overall | Nearly 25% |
| Weekly volume, December 2024 | Nearly 60% at the peak |
| Weekly volume, early October 2025 | About 20% |
| Sports volume, all time | 45% |
| Election volume, all time | 17% |
| Politics volume, all time | 12% |
| Crypto volume, all time | 3% |
The authors report that the suspicious pattern began trending upward in July 2024, remained elevated through late April 2025, then subsided before rising again by early October. The category figures are estimates of volume classified by the model; they should not be read as established fraud shares.
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Wash trading generally means transactions arranged to create the appearance of trading activity without a bona fide net change in position. The 2025 authors look for networks of counterparties that trade heavily within relatively closed clusters and less with the wider market. Their method estimates each wallet’s tendency to close positions, then iteratively updates scores using a volume-weighted network of counterparties. It also selects thresholds for individual markets.
The paper considers patterns such as triangular trades, chains, and clusters. Direct stablecoin transfers and shared display names are used as auxiliary evidence for some wallet groupings. These signals can identify behavior consistent with wash trading, but they do not by themselves establish that wallets share an owner or that a trade was deliberately fraudulent. Legitimate automated market making and other lawful activity can also complicate classification.
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The authors state that “there is no definitive ‘ground truth’ proving whether a transaction is a wash trade.” The near-25% estimate is therefore a model classification, not an adjudicated count of proven violations. It also depends on the algorithm, market-specific thresholds, sample period, and the definition of volume used.
Why a 2026 study reports just 0.22%
A separate analysis by Zhiyi Lyu, described in the wash-replication-2026 repository, reports a 0.22% wash-trading rate by trade count: 37,786 flagged trades out of 16,959,221. Its panel covers 199 Polymarket V1 NegRisk markets from January through December 2024, with the study panel closing on December 7.
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That figure does not directly contradict the 2025 estimate. The studies cover different portions of Polymarket and count different things: the 2025 paper reports estimates based largely on volume across a broad platform sample, while the 2026 analysis reports the share of trades flagged in a restricted market panel. The repository notes that its panel excludes much of Polymarket’s universe, including Sports and Election markets, where the 2025 paper estimated especially high activity.
| Study | Markets and period | Reported denominator and result | What the figure represents |
|---|---|---|---|
| Sirolly, Ma, Kanoria, and Sethi (2025) | Broad Polymarket sample, November 21, 2022–October 12, 2025 | Nearly 25% of historical volume | Volume estimated by the authors’ network-based algorithm to be likely wash trading |
| Lyu (2026), as described in the replication repository | 199 V1 NegRisk markets, January–December 2024; panel closes December 7 | 0.22% of trades (37,786 of 16,959,221) | Trade-count rate for the restricted panel |
What Polymarket says it does about manipulation
Polymarket’s official transparency page says wash trading, spoofing, and other potential market manipulation are prohibited and monitored. The company describes using custom machine-learning models, commercial blockchain analytics, trade-surveillance tools, open-source research, and human referrals. It says substantiated matters can lead to wallet restrictions, legal action, or referrals to law enforcement.
Those statements describe the platform’s own policies and processes; they are not an independent audit showing how often manipulation is detected or how effective enforcement is.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How to interpret the headline
- “Full of” is too broad if it implies proven fraud. The 2025 study identifies suspicious patterns, not confirmed intent or common control for every flagged wallet.
- The headline estimate is time- and category-dependent. The authors report a peak near 60% of weekly volume in December 2024, but a much lower estimate for Crypto than for Sports.
- The 0.22% result has a narrower scope and a different denominator. It concerns trade count in 199 V1 NegRisk markets, not all Polymarket volume.
- The platform says manipulation is prohibited and monitored. Its disclosure does not independently establish surveillance effectiveness.
For a reader deciding what the evidence supports, the defensible conclusion is that one broad, model-based study found a substantial amount of trading behavior consistent with wash trading, with large variation by time and category. The available studies do not establish a single verified percentage of Polymarket activity that was fraudulent.
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