Twitter's user base grew 33% last month, according to analytics firm Compete and at the current growth rate could top 100 million users by the end of the year.
The site has nearly 8 million users in the US alone, said Compete, with US visitors growing 964.5% in the past 12 months.
Social Times founder Nick O'Neill said he estimates Twitter's global customer base to be around 10 million. At this rate of growth Twitter could top 100 million before 2010, O'Neil said, but added that a more realistic estimate will be 50 million users by the end of the year.
The average Twitter user spends more than nine hours on the site per month, Compete said, and accesses 12.7 pages per visit.
Late last year, Twitter rejected a buy-out offer from Facebook, turning up its nose at the $500 million stock offer despite the fact that it had yet to develop a revenue-generating business model. Last month, Twitter raised $35 million in a third funding round.