Chief Executive Officer Steve Ballmer, when asked whether he would consider acquiring Twitter Inc., said the value of owning the company wasn't clear. "We have a great relationship, partnership with Twitter," Ballmer said Tuesday at the Search Marketing Expo in Santa Clara, Calif. "I would hate to not have that partnership. Whether we need to own them or not is far less clear."

Twitter, the third-largest social-networking site in the U.S., has a lot of appeal to users as an independent company, Ballmer said. Microsoft, the world's largest software company, announced last year that it would offer Twitter's short messages on its Bing search-engine site.

Twitter co-founder Biz Stone said in November that his company isn't for sale and may eventually be taken public. San Franciscobased Twitter ranks behind Facebook Inc. and News Corp.' s MySpace in U.S. social-networking users.