Yahoo's new search-based advertising model will debut Feb. 5, a month earlier than its previously announced release date, the company said Wednesday.

Code-named "Panama," the system will rank ad results based on both the fee paid and their relevance to the search. Earlier versions of the ad word system ranked advertisements solely on the basis of the fee paid. Yahoo did not announce the system's official name.

Selected advertisers in the U.S. will receive invitations to upgrade to Panama during the first quarter of 2007 as the company aims to have all existing advertisers upgraded by the end of the quarter. Similarly, selected non-U.S. advertisers will begin to receive upgrade invitations in the second quarter of this year on a market by market basis, the company said.

The search pioneer is looking for new ways to regain ground lost to rival Google. In December, 2006, Google accounted for 47.3 percent of all online searches conducted in the U.S., according to rankings by comScore Networks. By contrast, Yahoo placed a distant second with 28.5 percent of U.S. searches.

The new ad system falls under Yahoo's Advertiser & Publisher Group, now led by the company's former Chief Financial Officer Susan Decker, as part of a reorganization into three main groups that the company announced December 2006.

On Tuesday, the company beat Wall Street projections for its fourth quarter 2006 earnings and revenue with total quarterly revenue of $1.702 billion.