Marketers can share stories both good and bad about working with ad networks, but a new study indicates that using an ad network may offer no benefit to brand marketers whatsoever.

The report, "Improving Ad Performance Online," from the Online Publishers Association (OPA) found that ads bought through networks and appearing on portal websites performed significantly worse than premium ads sold on content websites.

Ad awareness was 21 percent greater for ads on content sites when compared to portals, and 50 percent greater than inventory sold through ad networks, according to the study. Video ads appearing on content websites were the most effective.

The OPA's report comes at a time when spending on display is expected to drop 17 percent by the end of the year, according to The Wall Street Journal. A few weeks ago, reports surfaced that ad network CPMs were on the rise, but some attributed this to the tough time publishers were having selling their premium inventory, therefore turning to ad networks.