US research firm comScore has published its latest Video Metrix online video rankings for the US, with Google sites (i.e. YouTube) still far and away the leader with 150.3m unique viewers in September watching 13.1bn videos. After Yahoo sites and AOL, Vevo takes fourth place in the rankings with 50.3m unique US viewers and 741.3m videos watched, at an average of 38.7 minutes per user. That’s up from the 44.8m unique viewers reported by comScore for July (Bulletin, 20-Aug-12), although Vevo has been stressing that comScore doesn’t track all its views and viewers in the US, due to growing mobile usage. comScore is on more solid ground with its analysis of the top YouTube Partner Channels though: it notes that Vevo had 48.8m viewers watching 545.4m videos on its YouTube channels in the US in September, taking top spot ahead of Warner Music Group’s 24.4m viewers watching 133.7m videos.