UPDATE: Google has announced All Access, a streaming music service. Click here for the story with a list of announced features.

Google (NASDAQ: GOOG) is expected to announce a streaming music service today at the Google I/O keynote in San Francisco.

Could the Mountain View, Calif.-based tech giant unseat the most popular streaming services? Google's service would compete with Spotify and Rdio but will not offer a free option, the New York Times reported.

Spotify has more than 24 million regular users, but only about 25 percent of them pay for the service. Plans are expected to start at $5. Pandora, its largest competitor, has more than 200 million users, most of whom do not pay for a premium plan.

Streaming music revenues still pale in comparison to music services like the Apple Store, but they are expected to rise more than 40 percent this year, according to Juniper Research.