Riding a surprising ratings wave for what was already one of its most popular series, Showtime has greenlit a fourth season of "The L Word."

The premium-cable network has ordered 12 more episodes of the show, which began its third season of exploring the lives and loves of a group of lesbian and bisexual L.A. friends last month. Production on the new season will begin next summer, with an airdate likely in 2007.

"'The L Word' without a doubt is one of Showtime's true signature series," says Robert Greenblatt, president of Showtime Entertainment. "We've seen a ratings explosion in season three, the likes of which we would never have predicted. Clearly something has caught fire, and we want the fourth season in production as soon as possible."

Showtime doesn't release specific ratings figures, but the network says viewership for "The L Word" are up by better than 50 percent over last season's first few episodes.

The show picked up its first Emmy nomination last year -- a guest-acting nod for Ossie Davis, who played father the father of Beals' and Grier's characters.