Microsoft (NASDAQ: MSFT) and Yahoo (NASDAQ: YHOO) Gain Search Market Share

Both Yahoo (NASDAQ: YHOO) and Microsoft (NASDAQ: MSFT)’s search engines have gained market share during the month of May, according to a report from comScore, marking the third consecutive month that Google has seen a decline in its market share.

Yahoo took 18.3% of the search market in May compared to 17.7% in April. Microsoft’s Bing jumped to 12.1%, up from 11.8 in April. America Online’s search engine dropped from 2.4% to 2.3%. Google’s numbers dropped from 64.4% in April to 63.7% in May.

Microsoft and Yahoo are planning to partner in a revenue-sharing arrangement in which Yahoo will sell ads across both networks and Microsoft will concentrate on users’ online search and buying habits.

Some analyst aren’t so sure about comScore’s numbers though. Ben Schachter of Broadpoint Amtec wrote in his report that comScore’s methodology and definitional changes have affected the usefulness of the reported data. He noted that Microsoft and Yahoo made use of a number of “contextual shortcuts” on their homepages which may have skewed the monthly comScore data for May.