Supernatural leads in ads and in-house promos.
From TVGuide.com:
"[…]I surfed around and couldn't find the CW's overall average, but as far as specific programs go, Supernatural is a most dubious No. 1 (tied with What About Brian) among all network offerings, ceding a full 17:50 of each hour to ads and in-house promos. In other words, nearly 30 percent of each Supe' hour has nothing to do with those Winchester boys. Who's the real demon now?[…]"