But as much as 80 percent of online ad inventory actually goes unsold, Thomas Weisel's Mr. Boyle says. Leading Web Advertisers examined 20 of the top Web sites for advertisers, as measured by the New York consulting firm Media Metrix between January and mid-June this year. On average, about 22 percent of the ads on those sites were house ads, the survey found. No comparisons were available for the year-earlier period. In that way, the house ads are one signal that a site is losing out on revenue.
Some portals are especially fond of house ads.
It's impossible to sell every single ad. Self-promotion Dick Gourley, vice president for worldwide sales and marketing for Talk City Inc., of Campbell, Calif., says as much as 25 percent of the ads on the site might be house ads because the site is trying to promote different areas, including health and family sections. A Netscape spokesman said ad revenue has been growing. Banner ads' effectiveness has been in question ever since advertisers came to the Web in 1995. But outsiders can't know for sure how much ad space is available on a given site.