Music sites are fighting to be free More try out ad-supported free conten

LOS ANGELES — There's a new music revolution brewing, and it's social.

Social music sites Imeem and Last.fm — which offer on-demand, ad-supported free music — have grown rapidly to 20 million monthly users each. Their success has the music industry seriously exploring the viability of ad-supported, free music as the next big business model for online music.

"This is driven by the reality of the way the Web is working now, and the amount of advertising dollars moving to the Internet," says Rio Caraeff, executive vice president of eLabs, Universal Music's digital arm. "This is about going where the money is and where the fans are, and giving customers what they want, which is free music."

In the wake of declining CD sales, the music industry has struggled with new ways to market music online. Apple's iTunes store is one powerhouse, with ...