One-fifth of paid search clicks in the last quarter of 2012 came from mobile devices, which also accounted for 15% of retailers’ paid search spending in Q4, says digital marketing agency Rimm-Kaufman Group in a new report analyzing data from its clients worldwide, which include retailers. Spending for paid search ads on tablets increased 187% year over year, marking the seventh consecutive quarter that it outpaced smartphone paid search spending growth, which was up 178% year over year, RKG says. Desktop paid search spending increased 11% year over year.

The most popular tablet among ad-clicking consumers, the iPad, has been losing some of its dominance, despite more consumers responding to paid search marketing on tablets, the report says. Competing tablets claimed nearly 16% of tablet traffic in Q4, up from 7% in Q4 2011, it says.

Additionally, RKG says Google Inc.’s and Microsoft Corp.’s Bing search engines in Q4 both drew increased paid search spending from retailers and more ad clicks, and charged more per click. Paid search spending on Google increased 19% year over year, with 14% more ad clicks and a 3% increase in cost per click. Paid search spending on Bing was up 54%, with 39% more ad clicks and an 11% increase in per-click cost, RKG says.

Search marketing agency Covario Inc. reports similar findings about paid search spending for mobile devices, tablets in particular. Among its technology, consumer electronics and retailer clients in Q4, Covario also finds that paid search spending on Google increased 13% year over year. Meanwhile, on Bing paid search spending rose 23% year over year, but decreased 6% from Q3 2012, it says. On Chinese search engine Baidu, paid search spending was up 52% year over year. Baidu accounts for 23% of the world’s clicks altogether, the agency adds.

Paid search spending in the Americas, led by the United States and Canada, was up 21% year over year in Q4; in Europe, 10%; and in Asia/Pacific, 13%, Covario says. The latter region’s paid search spending is the most volatile, the agency says—Q4 spending was down by double-digits from the previous quarter—but the authors say that Asia/Pacific still offers paid search marketers big opportunities.