Under that valuation, Facebook would be worth as much as $10 billion.
Google, meanwhile, also is reportedly interested in a closer relationship with Facebook.
Spokespeople with Facebook, Microsoft, and Google declined to comment when asked about the report.
In late 2005, Google bought a 5% stake of AOL for $1 billion. The deal made Google the search advertising provider for AOL.
Since then, the price of eyeballs has risen. A year ago, Yahoo reportedly offered $1 billion to acquire all of Facebook and was turned down. Mark Zuckerberg, Facebook's CEO, has stated that he wants to keep his company independent.
A previously published Wall Street Journal report claims that Facebook is on track to generate $30 million in profit this year from $150 million in revenue, about half of which comes from display ads provided by Microsoft.
Even as it entertains offers from Google, Microsoft, and potentially other online ad companies, Facebook is reportedly developing its own advertising system that will target ads based on users' profile information.
Not to be outdone, Google is reportedly planning to expose user profile information from Orkut, Google's social networking site, and iGoogle, its personalized information service, to programmers through an application programming interface. This would allow developers to make use of Google's social data in their own applications, just as they can do with Facebook's profile data if they use Facebook's development platform.
Facebook boasts more than 42 million active users, a number which has been growing at a rate of 3% per week since the beginning of the year.
Microsoft shares rose 1.5% to $29.08 on the news.