Various advertisers and search agencies continue to report an equal or higher return on investment on paid search campaigns that run on MSN's adCenter versus Google and Yahoo.

Search marketing firm, New York, found that campaigns on converted the best during March, scoring at 100 percent, followed by Overture at 97 percent and Google at 91 percent.

After a year of testing, MSN officially launched its paid search ad program in May 2006. Starting with about 2,000 advertisers in May 2005, about 10,000 now use adCenter, said David Jakubowski, general manager of Microsoft adCenter.

"We're really happy to have a third major player," said Peter Hershberg, managing partner of search marketing firm Reprise Media, New York. "It has really benefited our clients' campaigns."

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