On-demand music streaming site MOG has launched a free, ad-supported version of its service, the company announced today, providing access to its 11 million-song catalog in accordance with a particular user’s ability to make use of social networking.

While clearly a shot across the bow to Spotify — previously the only on-demand service to offer a free option on these shores — the new MOG service, dubbed FreePlay, is just as notable for applying a videogame-like model to determine real world rewards.

When users sign in, they’ll find a “gas tank” on the upper-left corner of the page, denoting how much free music remains available to them. To refill the “tank,” users can create playlists, share music via Facebook or Twitter or refer friends.

In keeping with its game-like system (the company recruited personnel from the videogame world and recently converted to an HTML 5 interface), there will be “Easter eggs” embedded in the service, awarding more music for unannounced reasons.

According to company CEO David Hyman, “Tastemakers and influencers can easily get a lifetime of free on-demand music” through consistent engagement.

Spotify dabbled in such virality rewards during its July beta launch, awarding invitations through the Klout Perks platform, but MOG is the first music service to systematize them to this degree. FreePlay will be ad-free for the first 60 days. MOG’s two unlimited paid subscription tiers remain unchanged.