Online ad-optimizing service PubMatic is now publishing an AdPrice Index with the average rates collected for remnant ads by 3,000 Web publishers. These are the ads that sites place from the big ad networks when they cannot sell the inventory themselves at normally higher rates. Small sites (those with less than one million page views per month) command nearly three times as much per ad as large sites (those with more than 100 million page views per month): an effective CPM (cost per thousand) of $1.18 versus $0.38. The effective CPM across sites of all sizes is $0.49. All of these figures are for March, 2008. Ad rates are also growing faster for small sites, up 18 percent since January versus 12 percent growth overall.

The low average rates for large sites reflects the poor returns on social networks, entertainment, and gaming sites. Effective CPMs for social networks are amongthe lowest at $0.37 in March. But there is hope, that was up 69 percent from $0.22 in January.