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Fan Duel is in a fight with New York Attorney General Eric Schneiderman over whether it and rival Draft Kings can operate their businesses in the state. Fan Duel is so popular that its site had over 10 million unique visitors in September, a sign of how successful the company has been at adding customers. As one of the largest advertisers on television, it is getting results, at least as measured by traffic.

The Draft Kings audience is nearly as large, based on research from audience measurement firm Compete. Its unique visitor count was 8.9 million, compared to Fan Duel’s 10.3 million. Together, their audiences are larger than Time.com, at 18 million, one of the biggest news sites on the Web.

The Fan Duel and Draft Kings audiences are growing at a fast pace. In August, Fan Duel’s unique visitors count was 3.1 million. Draft King also had 3.1 million in unique visitors the same month. Presumably the growth is due to tens of millions of dollars in advertising. This has been boosted by the start of the NFL season. As the season moves toward the playoffs, the audiences are likely to surge. That was true last year, when the audience of both sites peaked in December.

The appeal of Fan Duel is easy to understand. The company said it will give out $2 billion this year, which is larger than the annual gross domestic product (aka gross state product) of Texas. Winning is almost instantaneous. The player picks a one-day game from any of thousands of leagues, which must be chosen under the salary cap provided by the site, and if the pick pays off, the money is paid the same week.

One reason the sites are so successful, so large and so well-visited is that they offer betting well beyond the NFL. Among the more than 20,000 leagues on which visitors can pick teams are MLB, the NHL and the NBA. For the time being, the only thing left that will knock down their traffic is the State of New York.

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