The report found that Americans conducted some 14.3 billion core searches in March, a 9 percent gain over February 2009. Some 9.1 billion of those searches were done on Google sites, while 2.9 billion were conducted on Yahoo and 1.2 billion on Microsoft.
"Searches for mapping, local directory, and user-generated video sites that are not on the core domain of the five search engines," the report mentioned, "are not included in the core search numbers."
Translated into market share, that means Google held 63.7 percent of the core search market in March 2009, a 0.4 percent gain from the 63.3 percent of searches done through its properties in the preceding month. Yahoo held 20.5 percent, down 0.1 percent, while Microsoft had 8.3 percent, a net gain of 0.1 percent.
Of the five "major search engines" that ComScore surveyed for the report, Ask Network and AOL LLC followed with 3.8 and 3.7 percent of the market, down 0.3 and 0.2 points, respectively.
In what is perhaps the beginnings of a bid to eat into Google's market share, Microsoft and Yahoo are reportedly in preliminary talks over a search and display advertising deal, following Microsoft's failed takeover attempt in 2008.
According to the Wall Street Journal, Microsoft CEO Steve Ballmer and Yahoo CEO Carol Bartz have been speaking about the possibility of Yahoo handling Microsoft's display advertising, while Microsoft takes over search advertising.
However, even if the two were to somehow join together on search, a report by The Nielsen Company found that their combined market share percentage would not be able to overcome Google's. In its report, Google finished first with 64.5 percent of the market, followed by Yahoo Search with 15.8 percent and MSN/Windows Live Search with 10.3 percent.
The Nielsen report also found that Google Search had expanded by 27.6 percent year over year, followed by Yahoo Search by 1.7 percent and MSN/Windows Live Search by 0.3 percent. As with the ComScore findings, smaller search engines such as AOL and Ask.com had comparatively miniscule market share.
Microsoft and Yahoo have been battling Google in a number of areas, including e-mail.