Technology correspondent, BBC News
MySpace is running out of breath, while Bebo and Facebook are fast catching up. That's the message from the latest figures on social networking in Britain.
MySpace is popular but other social sites are catching up
MySpace has long been the leading site for young networkers who want to run their social lives online.
But research firm Nielsen/NetRatings says May saw a drop in UK traffic to MySpace, while Bebo and Facebook continued to attract new users.
Facebook, once largely confined to American colleges, has grown its audience by more than 500% in the last six months - making it more popular in Britain than in the US.
Nielsen says 10% of UK internet users visited Facebook in May, compared to 9% of US online users.
Alex Burmaster of Nielsen/NetRatings says: "If the April to May growth rates were to remain consistent, both Bebo and Facebook would catch MySpace in September this year."
MySpace is still well in the lead with 6.5 million UK users, compared with 4 million for Bebo and 3.2 million on Facebook.
But the figures also show that MySpace is proving much less compulsive for its users than the other two sites.
Its users spent an average of 96 minutes on the site in May, while Bebo users were there for 152 minutes and "Facebookers" spent 143 minutes on their site.
There was also evidence that there is plenty of promiscuity amongst the social networkers - at least when it comes to visiting the various sites. Around half a million British users visited all three services in May.
But the battle to win the loyalty of this fickle crowd is hotting up.
In the last few weeks, Facebook has opened its doors to a crowd of outside applications and Bebo has announced plans to run its own TV mini-series on the site.
Rupert Murdoch, who bought MySpace in 2005, has already expressed concern about the growth of Facebook. His executives will now be under even more pressure to find ways of making MySpace fashionable again.