Google said Facebook.com is the leading Website in the world with 540 million unique users, reaching 35.2 percent of the total Internet population through April.
The social network, which boasts nearly 500 million total users, racked up 570 billion page views, according to Google's new DoubleClick Ad Planner 1000 list.
This list tracks the top 1,000 global Websites ranked by unique users and includes stats on each site's Web population reach, page views and whether the site has digital advertising. Google, angling for impartiality, did not include any of its properties in the study.
Yahoo.com, which boasts 600 million users, was not far behind Facebook with 490 million unique visitors, good for a 31.8 percent reach. However, Facebook dwarfed the Internet portal in page views as Yahoo notched 70 billion.
Microsoft, the company notorious for losing billions with its online services business, actually grabs more traffic combined than any Website in the world. The software company took three of the top six Web properties based on visitors.
Microsoft's Live.com grabbed 370 million uniques for a 24.1 percent reach, with 39 billion page views for April. Wikipedia.com was next with 310 million uniques, a 20 percent reach and 7.9 billion page views.
Microsoft's MSN.com portal nabbed 280 million uniques for an 18.1 percent reach on 11 billion page views. Microsoft.com landed 230 million visitors for the month, reaching 14.8 percent of the Web population with 3.3 billion page views.
Microsoft's Bing.com search portal was ranked No. 13, with 110 million unique, a 7 percent reach and 2.7 billion page views. In the search kingdom, Google still rules the roost. Twitter.com racked up 96 million unique visitors, reaching 6.2 percent of the Web audience and 5.4 billion page views.
Google culls the data from a number of computer, not human-generated, sources, an important distinction Google likes to make for propriety's sake.
These sources include: data from Google Toolbar users who have opted in to enhanced features, publisher opt-in anonymous Google Analytics data, opt-in external consumer panel data, and other third-party market research.
Google is also allowing advertisers to specify that they only want their content ads to show on these top 1,000 sites through its Ad Planner 1,000 targeting filter.
"This new feature will ensure that your ads reach a large number of users, but only on well-known sites best suited for branding goals," Google AdWords representative Katrina Kurnit explained.
Speaking of ad targeting, Facebook's user base and page views are big reasons why the ceiling is so high on advertising on Facebook.
The Nielsen Company and Facebook said ads with social context increase campaign effectiveness by making people more likely to notice the ad, remember its message and increase their intent to purchase.
Facebook is trying its hardest to maximize social ads on its network by opening up the little digital walls between users and their brands through efforts such as social plug-ins and instant personalization.
But users pushed back, citing privacy reasons, and a chastened Facebook changed its privacy settings again May 26.