Listen closely at the office, and you're bound to hear it a buzz of excitement one day, a cry of frustration the next.

Browse the magazine aisle at the grocery store, and you'll see it dozens of publications giving piles of information you never thought you would need.

It's confusing to the outsider, this fantasy craze that has swept the sports nation. But to those who've caught the bug, fantasy leagues are a way of life. And if history is any indication, it's only going to get bigger.

"You get them in one time, and people are hooked," said Brendan Roberts, a senior editor at The Sporting News. "They call it the crack-dealer mentality: Get 'em hooked the first time, and they'll play every year.

"It's a competitive game. People like to play it. It's about camaraderie and playing with your friends. It tests your knowledge and takes you deeper into the game."

A society obsessed with sports coupled with most fans' thirst for competition has made fantasy a smashing success.

According to a 2006 Fantasy Sports Trade Association survey, last year, more than 16 million Americans between the ages of 18 and 55 played in leagues ranging from football to auto racing to golf. What started as a way for a group of friends to more closely follow their sport of choice now is a multibillion dollar business.

The past

Tracing fantasy to its roots is not an exact science. There are stories of fantasy-like baseball leagues dating to the 1920s and '30s.

There was a group in California in the 1960s that called itself the "Greater Oakland League," which created a football competition that operated much like those of today. They drafted players, kept track of points and went head-to-head with other teams throughout the season.

Strat-O-Matic took hold in the '70s. The game, which had player cards that gave different statistics based on the roll of a dice, allowed fans to simulate multiple seasons, but it was not driven by actual, in-season statistics.

The real breakthrough for fantasy sports, especially baseball, came in 1980, when a group of New York journalists invented rotisserie scoring named for the New York City restaurant La Rotisserie Francaise, where they were eating lunch at the time the idea was pitched.

The rotisserie system assigned a point value to individual statistical categories, and the points then accumulated throughout the season.

Even with a method in place, though, fans still had to spend hours compiling stats and adding up points. It wasn't until the Internet took off in the mid-90s that fantasy really grabbed hold.

The present

Last fall, there were 25 different fantasy publications previewing the NFL. There were four breaking down the season on the field. There was a similar ratio for baseball this spring.

"Ten or 15 years ago, it was considered impure to play fantasy, now it's considered acceptable," Roberts said. "Even the old-timers, who've been following baseball for years, are playing.

"You don't have to be a baseball stat nut to enjoy the game. There are many different variations of set ups, from weekly leagues to daily-transaction leagues. It helps to be into the game, but that's not a necessity."

There now are an infinite number of Web sites hosting fantasy leagues Yahoo, Sportsline, Sporting news, Rotowire, ESPN and Fantasy 411. And new methods of scoring head-to-head and fantasy points have made leagues even more popular.

It's estimated that every year employers lose hundreds of man hours and thousands of dollars of production to fantasy. The FSTA survey reported the average player is in six leagues from various sports, spends three hours a week managing their teams and almost $500 annually to participate.

These are not social degenerates, either. These are college-educated professionals living in the suburbs with an average household income of $80,000.

So is this obsession a good thing? Well, the NFL, NBA and MLB never have been more popular, and the money-generating machine the fantasy industry has become is impossible to ignore.

"It's no coincidence that baseball is setting attendance records," Roberts said. "People are way more knowledgeable about the players than ever before. I think fantasy and online, the ability to get all the stats you'd ever want, have raised the awareness of the sport and made it a lot more popular."

Like in actual sports, though, football remains by far the most popular among fantasy users. Last year, 80 percent of players were in football leagues. Baseball was a distant second at 30 percent, followed by auto racing, basketball, hockey and golf.

The future

You might have seen the ESPN commercial in which Peter Gammons, John Kruk and Cincinnati Reds pitcher Bronson Arroyo stage a concert announcing that ESPN fantasy baseball is free.

As ridiculous as it seems, in 10 years, that commercial will be a landmark in fantasy sports history.

In the past, ESPN has allowed the smaller-revenue companies to remain players in the game. Now they're going after them.

"The growth is only going to grow," Matthew Berry, ESPN's senior director of fantasy sports, wrote in an e-mail. "It's going to get bigger and better."

How big can it get?

Jeff Thomas, who founded Sports Buff Fantasy Sports in 1993, doesn't see a ceiling.

"The game at the root of the popularity is the same," Thomas wrote in an e-mail. "Fantasy sports will evolve with new products, new software tools and new creative twists. We'll also see the large brands increase their investment in fantasy sports as they see its value as a promotional tool."

Added Roberts: "There are three ways to make money in this business: Sex, sports and gambling. Those are the ways you make money. Fantasy sports doesn't have anything to do with sex, but it has the sports, it has and the money."

And that, apparently, is what Americans are after.

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What are they playing?

According to the Fantasy Sports Trade Association, more than 16 million American adults participated in fantasy sports leagues in 2006. Here's what they're playing:

Sport Total* Pct.

Football 12.8 80

Baseball 4.8 30

Auto racing 4.16 26

Basketball 3.2 20

Hockey 1.92 12

Golf 1.12 7

* - in millions