Beginning today, much of America will become absorbed in a high-stakes game. Millions of dollars will change hands, workplace productivity will take a hit, morale will bounce around, and some people will wonder whether the whole country has gone bonkers.

Welcome to March Madness.

The term refers to the three-week NCAA men's basketball tournament. But it could just as easily refer to all the action that takes place off the court.

Whether it's five bucks in an office pool or a high-dollar auction where the bidding for the best teams reaches into the thousands, millions are expected to bet on the tournament. Add in the mushrooming presence of online gambling, big-bucks contests sponsored by sports bars and the lurking presence of federal agents, NCAA investigators and the IRS – and even the Super Bowl seems to fade in comparison.

"It is by far the biggest gambling event of the year," said Victor Matheson, an expert on sports economics at the College of the Holy Cross in Worcester, Mass.

This evening, when the NCAA announces the 65-team field, brackets showing first-round matchups will quickly turn into betting sheets, copied and recopied, burying offices under a blizzard of bets and generally bewitching and bewildering America for the next 22 days.

As many as 37 million people are expected to participate in the wagering, according to an estimate by Challenger, Gray & Christmas, a job counseling firm in Chicago.

No reliable statistic exists on how much money is gambled on the tournament. An oft-cited FBI estimate of $2.5 billion was dismissed recently by bureau spokeswoman Denise Ballew, who said the FBI has never done a study of sports gambling.

Las Vegas lawyer Anthony Cabot, an expert on sports gambling, estimated that Americans bet up to $100 billion on sports annually – and the two biggest events are the Super Bowl and the NCAA men's tournament. "There's no question that both of them are huge."

The typical office pool will generate a few hundred bucks for some lucky bloke. But there are also powerhouse pools that produce pots well into the five figures.

"We are aware of pools that can get up to $100,000," NCAA spokeswoman Stacey Osburn said.

One Dallas real estate developer said he won $16,000 – and didn't even pick the champion. On the day the brackets came out, he and a couple of dozen other high rollers got together for a Calcutta auction.

An auctioneer took bids for each team. Lower seeds went for $50 to $75, while tournament favorites attracted bids of several thousand dollars.

The developer said he spent "about four grand" on three of the four teams that eventually made it to the Final Four.

"It's great fun," he said, preferring to remain anonymous because he doesn't want to attract the attention of legal authorities.

A more typical March Madness bettor is Danny Grier. For the last 10 years, Mr. Grier, 42, has participated in an office pool at his job along with about two to three dozen co-workers. Players fill out a bracket and put $10 in the pot, he said. He's won four times, he said, but the money is almost an afterthought.

"It's fun and we have a good time doing it," he said while watching a game at Christies Sports Bar on McKinney Avenue.

Nearly half of all U.S. workers have participated in an office pool at some point, according to a recent survey by Spherion Corp., a recruiting and staffing company based in Fort Lauderdale, Fla. The survey found that 75 percent of those who participate in office pools spend less than $20 – while 8 percent said they spent $50 or more.

The fun quotient is one reason the tournament likely attracts even more gamblers than America's other mega-extravaganza.

"The Super Bowl is only a three-hour event, and there's really only one interesting result – who wins or loses," Dr. Matheson said. The Big Dance, by contrast, offers dozens of games to bet on over a three-week period.

Sports betting has grown so big that it has spurred the NCAA to increase its anti-gambling efforts. Among other things, all Division 1 basketball referees undergo background checks. Teams that reach the Sweet 16 in the tournament, and referees who work the games, are given an in-depth presentation on the dangers of sports wagering.

"A lot of times players are approached for information, and it's done in such a casual way they don't even know what's happening," said Ms. Osburn, the NCAA spokeswoman.

NCAA rules prohibit college athletes, coaches and administrators from participating in any kind of sports betting – no matter how innocent.

That's why former University of Washington head football coach Rick Neuheiselwas fired in 2003 for participating in a neighborhood betting pool for that year's NCAA basketball tournament.

The risks aren't very high for the average office pool participant.

Law enforcement tends to look the other way as long as the stakes are small and the person running the pool isn't taking a cut, according to someone in the Dallas County district attorney's office, who didn't want to be quoted citing a policy that's unofficial.

Federal law specifically prohibits Internet gambling, but that doesn't seem to deter folks from setting up NCAA betting pools on social networking sites such as Facebook. The people running those sites are exposing themselves to potential liability, Mr. Cabot said. On the other hand, cash prizes and other awards can be given away as long as the contests are free to enter, he said.

While many companies tolerate small-stakes office pools, productivity tends to slump during the tournament, according to studies.

"The annual distraction could cost employers as much as $1.7 billion in wasted work time over the 16 business days of the tournament," said the consulting firm Challenger, Gray & Christmas. That estimate is based on the amount of time spent on March Madness-related activities, including arguing with co-workers and watching games during business hours. It's also based on a conservative estimate that workers waste just 10 minutes a day on the tournament.

"Those who insist there will be no impact are kidding themselves," said John Challenger, the firm's chief executive officer. "It might be a slight drop in output or it could be slow Internet connections as bandwidth is sapped by employees watching streaming feeds of the games."

But the prevalence of office pools, adding to the growth of sports betting in general, including gambling online, has a dark side.

"During these kinds of periods in sports it's often the end of the rope for compulsive gamblers," said Charles Vorkoper, a gambling addiction counselor in Dallas. He noted that compulsive gamblers have high rates of suicide.

"They've been thinking that a big hit is coming. To get the big win, they'll take big risks. And when they lose, they've got nothing," he said.

Recovering gambling addicts also have it tough at such times, he said.

"These kinds of big sports events are highly promoted ... ."