You cannot bet legally on political races in the United States. But there is a thriving market in Britain and elsewhere for gamblers looking to make money on big races.
Many bettors are consuming a wide variety of data about the race between President Trump and Joseph R. Biden Jr. As a result, the betting odds can be a canary in a coal mine, picking up movements before some pundits notice.
On Tuesday night and Wednesday morning, political bettors, at least those in jurisdictions where they could legally place wagers, went on a wild ride.
Going into election night, bookmakers in places like Britain had Mr. Biden as a favorite, but were nonetheless more bullish about Mr. Trump’s chances to win than statistical sites like Fivethirtyeight.com and The Economist.
But the odds swung sharply on Tuesday night. As it became clear that Mr. Biden was underperforming in Florida, bettors shifted toward Mr. Trump, according to Oddschecker, an odds comparison site that does not take bets itself.
“The markets were twitching constantly,” said Pete Watt, the public relations manager at Oddschecker. By 11 p.m. Eastern time, the betting markets thought the president had a 69 percent chance of winning a second term.
Overnight, things shifted back to Mr. Biden as more votes were counted in Georgia and Arizona.
The betting will continue until it is clear who won. As of early Wednesday morning, betting markets had Mr. Trump around 25 percent to 30 percent to win— a bit lower than 24 hours before, but still a significant chance.