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As Fantasy Football leagues become mainstream hits, websites that host them are enjoying dramatic increases in traffic from passionate league members.

Sixteen million adults are expected to compete in fantasy football leagues this year, up from fourteen million in 2005, CNET reports. Fantasy football's growing popularity is a boon to host sites, such as CBS Sportsline, Yahoo, and ESPN.com. ESPN says its traffic for September was up over 17 percent from September 2005 totals, and executives credit the site's fantasy football leagues as being the prime driver of the increase.

Websites that host popular leagues benefit not only from a surge in traffic but also from the time that each user spends online. Fantasy football players tend to pour over statistics online, looking for any advantage they can gain over the competition. The Fantasy Sports Trade Association (FSTA) estimates that each player spends three hours a week researching players. Those are the kind of stats that sites like to show off to advertisers.

"Fantasy leagues are everything that brand managers and sports marketers would ever want," Jeff Thomas, committee chairman for FSTA, is quoted as saying. "Fantasy players are the most engaged consumer you can find."