The study also revealed that surfers spend two hours more during the month on gaming sites than other site categories, including porn, news, and sports.
Nielsen//NetRatings tracked the activities of more than 46 million users in the U.S. that availed themselves to the online gaming industry, among which middle-aged females outnumbered teenage boys, the research firm reports.
"Ranging from sites that offer original games to content sites that offer the latest information on popular console and PC games, the gaming industry's presence online is indisputable," said Kaizad Gotla, an Internet analyst for Nielsen//NetRatings.
Sites like Slingo, a popular site that offers users anything from bingo, poker, puzzles and trivia to cash prize games and casino, was determined by Nielsen//NetRatings to be the stickiest of all gaming sites on the web, averaging four-hour visits from surfers.
Close runner-up Electronic Arts managed to captivate surfers for an average of two and a half hours, and MSN Games, AOL Games, and Jigzone.com all averaged two-hour visits, or just under.
According to Business Week, video games are a bigger business than movies, measured by revenues, and online gaming is contributing significantly to overall industry growth.
In a report from tech industry data providers IDC, PC-based online games accounted for $450 million in revenues in 2003, an amount that is expected to more than triple by 2007 to $1.5 billion.