CBS, still riding a wave of success from its online coverage of the NCAA tournament, will advertise itself to marketers at this year's upfronts as the No. 1 television network on the web, according to a TVWeek report.

The average viewer stays on CBS.com for 17 minutes when watching online video, the longest time for any network, according to comScore. In March, CBS had close to 40 million streams of full-length episodes, clips and web-only content. The network also made more money in advertising revenue per online viewer than it did per television viewer when broadcasting March Madness basketball games.

"There is more and more of a microscope on performance this year," said Patrick Keane, chief marketing officer for CBS Interactive. "You have big brands that have moved beyond the test-and-learn phase into measurable large-dollar transitions [from the web to TV] this year."

CBS currently offers about 420 hours of programming across the internet, on CBS.com, YouTube, AOL and Joost. The network is also reportedly in discussions to bring its content to Hulu, a video-streaming partnership between News Corp. and NBC Universal. Hulu offers full length streams of Fox and NBC shows and has already sold out its ad inventory.