This is the blurb directly from XM concerning commercials:
Does XM have commercials?
All of the 69 music channels programmed by XM are commercial-free. Many of our news, talk, sports and entertainment channels (including comedy and kids), as well as four music channels programmed by Clear Channel Communications carry a limited amount of commercials. Most local radio stations carry 18 minutes of commercials every hour.
Do any music channels on XM have commercials?
Because of their early investment in XM, radio broadcasting company Clear Channel Communications programs four music channels (Nashville - Channel 11, Kiss - Channel 21, Mix - Channel 22 and Sunny - Channel 24). Clear Channel has the right to include commercials on the programming they provide XM. As a result, these four music channels carry a limited amount of commercials.
Does XM have commercial-free alternatives to the four Clear Channel music channels?
If you like the music on these channels: Nashville (Channel 11), Kiss (Channel 21), Mix (Channel 22) and Sunny (Channel 24), but would prefer a commercial free environment, we suggest the channels: US Country (Channel 17) plays commercial-free country superstars from the 80s and 90s; XM 30 The Hitlist (Channel 30) plays contemporary pop hits from today and the past few years; Flight 26 (Channel 26) plays modern pop hits from the 90s through today and Escape (Channel 78) plays beautiful music and easy listening favorites from the past fifty years.