Americans watched another record number of online videos in July with a total of 21.4 billion videos viewed during the month, according to the latest report from comScore.

In July, Google sites continued to rank as the most popular U.S. property with a record 8.9 billion videos viewed, making up 42 percent of all videos viewed online. YouTube accounted for more than 99 percent of all videos viewed at the property. Viacom Digital ranked second with 812 million (3.8%) followed by Microsoft sites with 631 million videos viewed (3.0%).

Fox Interactive Media, which includes MySpace Video, landed in the fourth spot with 558 million videos viewed (2.6%) and Hulu rounded out the top five with 457 million (2.1%).

More than 158 million Internet users watched an average of 135 videos during the month of July. Google sites surpassed its all time high with 121 million unique viewers during the month (74.1 videos per viewer), followed by Microsoft sites with 65 million viewers (9.8 videos per viewer) and Fox Interactive Media with 52 million viewers (10.8 videos per viewer).

Yahoo sites attracted 47.3 million viewers (7.9 videos per viewer) and Viacom Digital with 42.4 million viewers (19.2 videos per viewer).

ScanScout Network was the top video ad network with a potential reach of 80.1 million viewers, or 50.6 percent of the total viewing audience. Tremor Media landed in the second spot with a potential reach of 71.1 million viewers (44.9 percent penetration) followed by YuMe Video Network with 68.1 million viewers (43%).

Other highlights include:

• The top video ad networks in terms of their actual delivered reach were: Tremor Video Network (20.1 percent viewer penetration), Brightroll Video Network (17.4 percent), and BroadbandEnterprises.com (14.4 percent).
• 81.0 percent of the total U.S. Internet audience viewed online video.
• The average online video viewer watched 500 minutes of video, or 8.3 hours.
• 120.3 million viewers watched 8.9 billion videos on YouTube.com (74.1 videos per viewer).
• 48.2 million viewers watched 518.6 million videos on MySpace.com (10.8 videos per viewer).
• The average Hulu viewer watched 12.0 videos, totaling 1 hour and 13 minutes of videos per viewer.
• The duration of the average online video was 3.7 minutes.