The number of eligible products in Amazon.com Inc.’s Prime two-day-shipping-and-loyalty program increased 47% year over year to hit 33 million in the first quarter of 2015, according to a report today from R.W. Baird. Its latest Amazon inventory report also notes that total products carried by the e-retailer has surpassed 300 million for the first time.

Amazon, No. 1 in the Internet Retailer 2015 Top 500 Guide, added a musical sweetener to Prime when it launched Prime Stations in March amid continuing expansion of the number of products eligible for two-day shipping. Even so, the report adds that only 13% of physical goods in Amazon are eligible for Prime two-day shipping, “suggesting a meaningful opportunity for further Prime expansion.”

Prime Stations, an ad-free streaming web radio service, is available to consumers who pay $99 per year to join Prime or take out a free trial membership.

The Prime Stations service joins other program perks such as Prime Now one-hour deliveries in certain cities; original films via the Prime Instant Video streaming service; unlimited photo storage on the web; and some 1 million songs already available through Prime Music, which launched in June 2014 and remains available.

The radio service gives unlimited access to Prime Stations, which has ad-free music on the web and through the Amazon Music Desktop app (Mac and PC) and via an app for iOS, Android and Fire HD/HDX devices, an Amazon spokeswoman says. “There are hundreds of Prime Stations—Prime members just need to find a genre or artist they like and hit play to hear a continuous stream of music that can also be paused, replayed or skipped without any restriction. You can give songs a thumbs up or thumbs down; each station will adapt to the music tastes. A key difference is the lack of restrictions—no limits on skips, you can go back and forth, pause and replay.”

Prime Stations includes hundreds of stations that focus on such genres as rock from the 1980s and Americana, and such musicians and bands as Bruce Springsteen and Death Cab for Cutie.