Visitors to online gaming sites now number almost 217 million worldwide, representing year-on-year growth of 17 per cent, market researchers estimate.

The sector attracted 28 per cent of the total worldwide online population in May 2007 and recorded an average of nine visits per user, according to the latest comScore World Metrix study.

"The fact that these websites are pulling in over a quarter of the total worldwide internet population shows what a global phenomenon gaming has become, " said Bob Ivins, executive vice president and managing director of comScore Europe.

"The potential of the online gaming arena should be especially appealing for advertisers, as the average online gamer visits a gaming site nine times a month."

Yahoo Games was the most popular site, attracting 53 million unique visitors in May 2007. MSN Games followed in second place, having grown by 16 per cent since May 2006 to reach 40 million unique visitors in May 2007.

Both sites provide a mixture of strategy, trivia, arcade and board games, with puzzle and card games proving the most popular choices for gamers.

The fastest growing Top 10 gaming site was WildTangent Network, a US company that makes online and downloadable games, which grew by 398 per cent year-on-year to attract 11.5 million unique visitors in May 2007.

The site also attracted an average 12.2 visits per visitor, notably higher than any of the other top 10 gaming properties.

The popularity of gaming websites varied significantly between geographical locations. Yahoo Games dominated the North American and Asia-Pacific continents, registering 18.7 million and 20.9 million unique visitors respectively.

In Europe, however, Yahoo proved to be the fourth most popular gaming site with 8.6 million unique visitors.

MSN Games, the second most popular gaming site in the world, was the most visited site in Europe.

MSN Games was also more consistent in global geographical take-up, emerging as either the most or the second-most popular site in every geographical location.