Marchex Adhere's ad model

Local search and ad firm Marchex has added 23 websites to its Marchex Adhere platform, bringing the running total to 200 participating publishers.

The new websites include: Inc.com, UPI.com and NationalReview.com. Relationships have also been renewed with TheGlobeandMail.com and MotleyFool.com.

Marchex Adhere enables web publishers to sell text or display ad inventory, on their own, or with help from Marchex's sales team. They also have control over minimum ad rates, which advertisers appear on their sites, and the look and feel of ad units. Other publishers on the program include Investors.com (the online destination of Investor's Business Daily), Kiplinger.com and BusinessWeek.com.

The last several years has seen launch of a number of online-only content sites, many of which depend exclusively on ad revenue to stay afloat. Many such sites have turned to a multiplicity of ad networks in order to sell remnant ad space.

But a soured economy bodes poorly for the ad network market, which is saturated with companies that offer nearly the same services, according to GigaOM. What's more, online display advertising rates have begun to tumble.

Trends suggest less well-known ad networks will likely exit the market within the next year. Small online publishers with little brand recognition and no other viable revenue strategy will likely meet the same fate.