OK, so maybe not a huge surprise, but Google is said to launch a paid, subscription-based music service, like Rdio or Spotify, as soon as this week at the Google I/O conference, reports the Wall Street Journal.

According to “people familiar with the matter,” says the WSJ, the announcement of the new service could happen as soon as tomorrow, when Google hosts it’s annual I/O developer conference. The WSJ says that Google has previewed new music initiatives at I/O in the past, so it might just announce the streaming service there, as well.

The WSJ sources report that Google has already signed deals with Universal Music Group, Sony Music Entertainment and Warner Music Group to give customers access to certain libraries of songs for a fee.

Google also already has a music service, Google Music, which launched in 2011 as part of Google Play for Android devices. It has since expanded to a global service, including Australia, and includes a matching service like Apple’s iTunes Match service in the US.

The WSJ sources don’t know what the fee would be for such a service, or do they know if there will be advertising. Google makes most of its revenue from ads, though, so it seems like such a service would indeed include ads at some level, even a free one like similar offerings from Spotify, Pandora, and Rdio.

Last year, Google unveiled Nexus Q music and video streaming, though the launch of the oddly-shaped and confusing ball-shaped object was delayed due to lack of positive consumer feedback.

• SourceWall Street Journal
• ViaAndroid Police