The growing popularity of office pools, combined with dozens of dramatic games, has made the NCAA men's basketball tournament one of the most highly wagered sporting events of the year, second only to the Super Bowl.

Robaina said the amount of money legally wagered on March Madness games in Nevada casinos last year "was about $65 million." Super Bowl bets exceeded $70 million. But the number of illegal bets on the March Madness games dwarfs that total.

The FBI estimates that $2.5 billion was illegally wagered on the tournament last year, but Robaina said that figure may be too low.

"It's impossible to track the size and scope of illegal gambling, but generally you multiply the amount of money legally wagered by 50 to get a general estimate of illegally placed bets."

That would put the amount of money illegally wagered on March Madness this year at north of $3 billion.

Online pools have only fueled the betting frenzy., for example, an interactive sports and entertainment company, is offering $10 million to anyone who enters its online pool and correctly picks the outcome of all the games, said William Carey, Sandbox's COO and co-founder.

More than 615,000 contestants filled out Sandbox's online brackets last year, all of whom were eliminated by the end of the second round. That isn't surprising, considering there are about 9 quintillion possible outcomes.

Pretty good odds for Sandbox, especially since its online pool is expected to generate $3 million in direct marketing and advertising revenue this year.

Popularity surge

Some basketball fans and analysts believe that 1985 was the year March Madness and its pools began surging in popularity. That's when the NCAA expanded the field of teams from 48 to 64, meaning millions of more people across the country have some sort of connection to at least one school in the tournament.

Increased TV coverage has also dramatically boosted the popularity of NCAA pools. CBS which recently signed an 11-year, $6 billion contract with the NCAA for the rights to televise the tournament airs the games from early in the morning until late at night during the first four days of the tournament, with only a few 30 or 40 minute breaks between games.

"It's literally all hoops, all the time," said Mark Edwards, one local March Madness fanatic.

Edwards said the timing of the tournament also encourages betting.

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