ACDC: 23% of Major Election Contracts Showed Price Spikes

A new analysis by the Anti-Corruption Data Collective, or ACDC, found that 38 of 167 major congressional election contracts experienced price spikes of at least 30 cents. The study examined markets on Kalshi and Polymarket International that were worth more than $100,000. These sudden jumps can temporarily make a candidate look more likely to win than the actual support level suggests.

The research highlights a growing concern in the $47 million Los Angeles mayoral race, which became the most heavily traded mayoral contest of 2026. Spencer Pratt, a former reality television star, was heavily favored by prediction markets ahead of the June primary. One market assigned him a 78% probability of advancing to the November runoff. However, voters chose differently, and Pratt finished third in the primary.

ACDC data shows that shifting odds is inexpensive in less active markets. The group analyzed 18,000 active congressional markets across Polymarket International, Polymarket U.S., and Kalshi. They determined that 88% of these markets could have their prices moved by 10 cents with a single wager under $1,000. This accessibility allows individual traders to influence the perceived momentum of a race with relatively small amounts of capital.

Specific examples illustrate how these spikes function. In the Los Angeles race, a trader spent $1.25 million on contracts favoring Pratt on May 20. That trade pushed the price of Pratt’s victory contracts from 29 cents to 45 cents within seconds. While the price initially reverted, ACDC found it remained three cents higher for about two hours. Robert DeNault, head of enforcement at Kalshi, noted that rational traders often correct such anomalies. He stated that by the end of the day, the price was lower than when it began.

A similar pattern occurred in the Illinois Senate race. On March 3, a buyer spent $5,000 on contracts for Juliana Stratton, pushing the price from 47 cents to 79 cents. The price dropped back down but then spiked to 99 cents after another $3,000 in purchases. It eventually settled at 52 cents, leaving the market five cents higher than the starting point. Stratton won the Democratic primary two weeks later. Her office pointed to a concurrent poll showing her leading, though she declined to comment on the trading activity.

The discrepancy between market odds and polling results influences voter perception. A September study funded by the Brennan Center for Justice surveyed 1,994 registered voters. The data showed that voters were 10 to 20 percentage points more likely to believe a candidate would win if prediction markets favored that candidate, regardless of polling data. This effect persists even when the markets are wrong.

Kalshi and Polymarket have introduced tools to address these concerns. Kalshi added labels for markets with low trading activity and live feeds of individual trades earlier this month. Polymarket launched a surveillance system designed to detect attempts to manipulate election markets. Both platforms are regulated by the Commodity Futures Trading Commission, which oversees rules to prevent market manipulation and insider trading.

Despite regulatory oversight, identifying the traders behind large spikes remains difficult. Shana Bautista, head of global intelligence at Polymarket, explained that accessing detailed information on specific transactions often requires legal process. She noted that Polymarket partnered with Chainalysis in April to track suspicious trading on its international platform. This partnership helps identify unusual patterns, such as wallets that consistently win without losing.

The volume of money flowing into election contracts has surged. Wagers on the 2026 congressional elections have more than tripled the amount bet on the 2024 races, according to ACDC. Kalshi reports that viewers of its midterm election markets outnumber actual traders by a ratio of five to one. This shift suggests that many people are using these platforms as a source of information rather than just as a betting tool.

Kalshi maintains that its markets remain accurate over time. The company stated that in U.S. elections since 2024, candidates favored by its markets won roughly nine times out of ten. The Washington Post reviewed 268 candidates who received a 70% to 80% probability of winning on Kalshi or Polymarket in the two months before their primaries. Three-quarters of those candidates went on to win their nominations.