Google's results are in line with general internet use for May, which surged to 772m people online worldwide, an increase from 766m in April.
This represents a 16% penetration of the worldwide population of individuals age 15 or older.
The top three properties each boasted more than 20 average visits per visitor in May. These were Google with 27, Microsoft with 23, and Yahoo! with 22.
The fastest growing property in the top 10 most-visited sites was Apple, to which total worldwide visits grew by 5%.
ComScore also released data on the top 10 fastest growing sites. At number one is the price comparison group Ciao Sites, visits to which increased by 31% to 29.6m.
This has been put down to the occurrence of Mother's Day in several countries, with Priceline.com also posting a substantial growth of 15% to 23.1m visitors.
Facebook was the second-fastest growing site in May, increasing total worldwide traffic by 22% to 47m unique visitors. The social networking site receives 20.6 visits per user, equating to at least five times more visits per user than any of the other top-10 fastest growing sites.