Yahoo's share of search ad spending grew against rival Google but lost ground in its share of searches, according to a pair of new studies.

In the first three months of 2008, search spending by selected advertisers on Yahoo grew to 23 percent of the market compared to historical levels of 18 percent to 19 percent, according to search advertising technology firm SearchIgnite.

Google's search advertising market share fell to 71.1 percent from 74.9 percent during the period.

SearchIgnite's result may not necessarily be representative of the overall market. The company places search ads using various web portals including Google, Yahoo, and Microsoft.

Meanwhile, a separate study released today found that Google's market share of searches grew while Yahoo's share fell.

ComScore, an internet data researcher, said Google's sites received 59.8 percent of searches in March from among the top five search engines. The results were an improvement from the 59.2 percent market share it had in February.

Yahoo's search share fell to 21.3 percent in March compared to 21.6 percent the previous month. Microsoft sites were down to 9.4 percent from 9.6 percent. AOL sites were down to 4.8 percent from 4.9 percent. Ask Network sites rose to 4.7 percent from 4.6 percent.