• by Laurie Sullivan  @lauriesullivan, January 22, 2015

Google continues to lose search market share to Bing and Yahoo, albeit slowly. Data firm comScore and media agency Merkle RKG report a decline in organic and paid-search market share, respectively.

Google sites led the U.S. explicit core search market in December with 65.4% market share -- down 1.6% -- followed by Microsoft sites with 19.7%, up 0.1%; and Yahoo sites with 11.8%, up 1.6%, per comScore.

Marketers working with Merkle RKG spent 1.3% less to buy search ads running on Google in the U.S. during Q4 2014, compared with the year-ago quarter. The company's share of ad-click volume fell nearly 2% during the same period, per a quarterly report published Thursday.

For the sixth consecutive quarter, Merkle RKG saw less than 5% growth in cost per click (CPCs) for Bing Ads, among its clients. In Q4, CPCs rose 3% year over year (YoY), but click volume rose 27%, driving total spend by 31%. Bing Ads benefitted from recent deals to provide mobile search ads to eBay beginning in late Q2 2014, and then Yahoo becoming the default search option for Firefox in December, but the increase in mobile volume put pressure on CPCs.

After becoming the default Firefox search provider in early December, Yahoo’s share of total U.S. Firefox traffic grew from 12% to 30%, but Firefox users have been switching back to Google. This means Yahoo stands to gain just 2% or less U.S. paid search share from the deal, per the Merkle RKG report.

"Some might be surprised that Yahoo's deal with Firefox hasn't worked out better, but if they only keep 2% of the search market, it's a pretty big deal," said Mark Ballard, director of research at Merkle RKG.

Yahoo Gemini in Q4 accounted for 27% of all mobile Bing and Yahoo ad clicks for advertisers. Bing Product Ad share doubled from Q3 to Q4, accounting for 7% of all Bing Ads paid-search clicks for participating retailers. Product Ads produced 14% of non-brand clicks among the same programs, per the report.

Not all bad news for Google. Overall, Google paid-search clicks rose 12% YoY in Q4 and CPCs rose 7%. The product listing ads (PLA) format continued to take Google search volume share from text ads in Q4, reaching 30% of all retailer ad clicks. Google turned up the heat on PLAs, giving them greater prominence in 2014 by often serving them above organic listings, rather than confining them to the right rail, per the report.

Among non-branded Google search ads, PLAs generated 56% of retailer clicks in Q4. Google PLAs produced click-through rates 130% higher than for non-brand text ads in Q4. The return on investment also remained 9% higher than non-brand text ad ROI for the typical retailer, despite average order value continuing to run 12% lower, per the detailed report.