Isobar's Carat Interactive and Mediaedge:cia's Outrider have qualified as strategic providers under Yahoo's search advertising reseller program, AdWeek writes. Yahoo's Ambassador program is designed for agencies that resell all of Yahoo's search marketing products, including keyword and paid inclusion listings, local search and marketing tools.

Both Yahoo and Google have reached out to agencies; search marketing now accounts for about 40 percent of online adspend and is often being included in overall online ad plans.

Yahoo opened up the four-year-old Ambassador program, which had focused on search engine marketing firms, to ad agencies last October. It issued a study this week showing that display ads influence search behavior.