The launch of Windows Vista has lifted Microsoft's Live Search share of the U.S. search market, but Microsoft's gain has come at the expense of Yahoo and Ask rather than Google.

"We saw a pretty substantial lift for the first time this year for Live Search," says Jeremy Crane, director of client services at Compete, an online market research firm. "And it happened to coincide with the consumer launch of Vista."

Live Search is the default search engine in Vista, a home-field advantage that Google has sought to counter with distribution deals for its search software.

In a blog post published today, Compete reported that Windows Live had received almost 590 million Web search queries in the United States in February, a 10% increase from 534 million in January.

During this period, Microsoft also saw a 10% increase in search query volume, which translates to a market share gain of 1 percentage point, moving Live Search from 8% to 9%.

Google also saw a market share gain of 1 percentage point during the same time frame as a result of a 3% gain in overall search volume, which reached almost 4 billion queries. Google's share of the U.S. search market in February rose to 63% from 62% the previous month.

Yahoo and Ask lost market share during this period, dropping from 23% to 21% and from 4% to 3% respectively. Yahoo's market share loss of 2 percentage points was the result of a 7% drop in search volume. Ask's market share loss followed from a 5% decline in search volume.

Last month, comScore Networks reported that Google had captured 47.5% of the U.S. search market in January, a significantly lower percentage than Compete counted. comScore also noted that Yahoo's U.S. search share dropped to 28%, Microsoft's rose slightly to reach 10.6%, and Ask's declined to 5.2%.

Crane attributes the difference in statistics to different methodologies. comScore, he says, includes a variety of online properties such as video search in its search numbers, whereas Compete only counts Web search.