The ad-tracking service PubMatic reported that the cost of online advertising showed a slight decline, of less than one percent, for the third straight month. The sites surveyed by PubMatic are not search engines, but content publishers that derive at least some of their revenues from advertising.

Apparently reflecting weakness in the overall economy, the PubMatic AdPrice Index tracked more dramatic declines in advertising costs on News websites, and Gaming sites. Entertainment was the only category to buck the downward trend.

Social Networks, already the lowest performing category, fell another $0.05, going from $0.32 in May to $0.27 in June.

Rajeev Goel, cofounder and general manager of PubMatic, noted "Online advertising is in a holding pattern like many sectors of the US economy."