The American Gaming Association (AGA) expects $93bn (€82bn) to be wagered illegally during the new NFL American football season as it described US prohibition as “failing”.

The US trade group said that 97.8 per cent of an estimated $95bn in bets will be made with unlicensed operators or outside of the four states in which sports betting is legal – Delaware, Montana, Nevada and Oregon.

The AGA commented in the same week that New Jersey began another appeal against the 1992 federal law that bans sports betting, continuing a four-year battle.

Geoff Freeman, president and chief executive of the AGA, said: “Illegal sports betting is reaching new heights of popularity in America. It’s clear that a federal ban on traditional sports betting outside of Nevada is failing.”

The NFL season began last night when defending champion New England Patriots beat Pittsburgh Steelers in the first of 256 games ahead of February’s Super Bowl. Last season’s final attracted $3.8bn (€3.4bn) of illegal bets according to AGA figures.

The AGA warning comes as daily fantasy sports (DFS) sites continue to grow, with operators such as DraftKings and FanDuel protected by provision of the 2006 Unlawful Internet Gambling Enforcement Act (UIGEA).

Referring to the appeal rejection in New Jersey, Freeman said: “With Americans betting at least $140bn on sports illegally each year, it's clear that current law is not achieving its intended result.

“As the AGA leads an industry-wide task force to study sports betting, we will assess the implications of the court's decision as the gaming industry continues to develop innovative ways to provide products and experiences that meet consumers' demands.”