This isn't the first time Oprah has praised Microsoft's tablet. In early November, she announced that the tablet made her list of Oprah's "favorite things."
Twitter hasn't released an official Twitter client for the Windows store yet but as TechCrunch points out, it would have been possible for her to access the Twitter website from her Surface.
While it's unclear if Microsoft paid for Oprah's ringing endorsement, it should also be noted that Oprah included the iPad on her "Ultimate Favorite Things" list in 2010.
"Words cannot describe what I feel for this magnificent device. I really think it's the best invention of the century so far," she said of Apple's iPad at the time.
Microsoft did not immediately respond to a request for comment.
*Correction: An earlier version of this story stated Oprah sent the tweet Monday.