Also, as networks increasingly boost traffic to their Web sites via on-air and other promotion avenues, winners are emerging.

The ABC and NBC Web sites are consistently drawing much larger overall traffic than CBS and Fox sites. Both ABC.com and NBC.com are averaging 9.5 million unique visitors a month for October through December, while CBS.com is averaging 5.2 million unique users and Fox is at 2.8 million, according to Nielsen//NetRatings.

Regarding Internet streams of prime-time episodes, ABC.com led by large margins over the other network sites. In October, ABC.com streams of hits "Grey's Anatomy" and "Desperate Housewives" drew 3.1 million unique users, according to Nielsen//NetRatings. That dropped slightly to 3 million in November, then fell to 1.8 million in December, perhaps due to the inventory during the holiday season.

A cautionary note: the data only covers unique users, and many could be watching multiple episodes.

CBS.com, with shows such as "CSI" and "NCIS," trails ABC.com in second place, with 1.2 million unique users viewing full-episode streams in October--up significantly to 1.9 million in November, then down to 1.2 million in December, according to Nielsen//NetRatings.

Fox, despite hosting its Internet streams of "Prison Break" and "Bones" on its heavily trafficked sister News Corp. site MySpace, had 640,000 unique users in October--which increased to 676,000 in November and, like all networks in the rerun-heavy December, fell to 303,000 for the month.

NBC's streams did not have enough traffic to register on the Nielsen//NetRatings data.

All four networks employ some sort of advertising in their streams, ranging from a small "presented by (insert sponsor name here)" logo on the top of the screen on ABC.com to mid-roll ads on CBS.com to pre-roll on NBC.com and the Fox site. Advertisers include Allstate on ABC.com, AT&T on the CBS site, Cisco on NBC.com and Chase on Fox.

The streaming-video data may have some wrinkles. It is based on unique users visiting the access point (URL) for the videos on each network's Web site--dynamic.abc.go.com; cbs.com/innertube; myspace.com/fox; and nbc.com/video/rewind. Some individuals may have accessed the streams via another entry point, such as one attached to Fox's local station in New York.

NBC's low-level viewing of its Web-site streams of shows like "Las Vegas" and "30 Rock" comes despite heavy traffic to its Web site. There were 10 million unique users in October, according to Nielsen//NetRatings. That's as high as the weekly average for a top-40 show.

Still, ABC.com topped it with 10.6 million unique users that month, which increased to 11.7 million in November--as high as a top-30 show's weekly average. ABC.com widened its lead over NBC.com in November by almost 2 million unique users.

In December, however, NBC.com pulled ahead with 9.4 million unique users, compared to ABC.com's 6.3 million, according to Nielsen//NetRatings.

CBS.com drew 4.7 million unique users in October--up to 5.7 million in November and down to 5.1 million in December.

Fox posted 2.7 million in October, up to 3.3 million in November and down to 2.3 million unique users in December, per Nielsen//NetRatings.

But expect the "American Idol" phenomenon to boost Fox.com traffic through May.

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