The American Gaming Association (AGA) estimates that March Madness betting will exceed $10 billion on the upcoming 2018 NCAA men’s basketball tournament. Of that $10 billion, only about $300 million – or three percent – will be wagered legally through Nevada sports books.

Americans illegally bet at least $150 billion annually on sports, empowered by the Professional and Amateur Sports Protection Act of 1992 (PASPA), a failed federal prohibition on single-game sports betting.

Illegal wagering is often done through bookies, on illegal offshore websites, or through sports pools like popular March Madness basketball bracket pools.

According to a recent legal analysis, roughly two-thirds of states’ laws make it illegal to participate in sports pools, including filling out an NCAA tournament bracket, if there is money involved. Despite this, 10 percent of American adults, or nearly 24 million people, reported spending nearly $3 billion in the past year on college basketball pools alone.

More on March Madness betting at CDC Gaming Reports