MusicNet subscribers will have access to 75,000 songs
MusicNet, which is backed by Warner, EMI and Bertelsmann, is available through RealNetworks' new RealOne service from Tuesday.
The launch comes one day after Listen.com's subscription-based Rhapsody service went online, while Peter Gabriel's WebAudioNet is due to start later this month.
The remaining two major record labels, Sony and Vivendi Universal, will launch their version, Pressplay, early next year.
Convince fans
By then, music fans will have a wide choice of legitimate download sites through which to access almost any music they want.
But analysts are still unsure whether they will convince fans to abandon free song-swapping services in the Napster mould.
MusicNet subscribers will pay $9.95 (£7) per month to get 100 downloads per month from a choice of 75,000 tracks.
Madonna, The Beatles and Whitney Houston are among the artists who are on MusicNet's major label record companies. Subscribers will also get access to 100 webcast sources.
But no site will provide a comprehensive catalogue, regardless of record label, as Napster and other sites have done.
Jupiter Research's Mark Mulligan doubts the MusicNet offering is enough to woo consumers yet.
"They need to offer a greater choice of catalogue, if someone subscribes to MusicNet ...they will only have access to a limited amount of content," he told the BBC's World Business Report.
Crucially, consumers need to forget the "Napster phenomenon" and get used to the whole idea of paying for music online, he said.
"Online music users don't know whether they're listening to a Sony-published song or a Bertelsmann-backed artist," said Susan Kervorkian, an analyst with technology consultancy IDC.
"If they can't find a song on a site, they won't be coming back again."
IDC has predicted that the online music market is expected to top $1.6bn (£1.1bn) by 2005.
Another potential factor that may put users off is the fact that some services limit the way that songs can be copied on to portable MP3 players.
For example, Rhapsody's copy-protection system means a part of the music file remains on Listen.com's computers, meaning the user can only listen to the song on their computer.
Legal action
Free download services have continued to be popular - despite the fact that they are unauthorised and do not pay any royalties to artists, record labels and publishing companies.
Napster, one such site, started the online music boom and had 60 million users at its peak.
But it was forced to close after being sued by the American music industry.
Other sites have moved in to fill the gap - but they are slowly being targeted for legal action by record companies which have finally seen the potential of online distribution.