Google continues to lead the U.S. core search market with some 64.2 percent market share for its sites, according to a May 18 report by research firm ComScore.
Second behind Google's sites was Yahoo, which claimed 20.4 percent of the market, followed by Microsoft sites with 8.2 percent, Ask Network with 3.8 percent, and AOL with 3.4 percent.
Those numbers represented a 0.5-point gain for Google over March 2009. Both Yahoo and Microsoft declined 0.1 percent, while the Ask Network remained unchanged. AOL's market share was down 0.3 percent from March 2009.
Americans performed some 14.8 billion searches using the core search engines, an increase of 3 percent from March 2009. In gross numbers, Google sites accounted for 9.5 billion of these, Yahoo 3 billion, and Microsoft 1.2 billion.
Given the size of its market share, Google recently launched a campaign to convince politicians and media types that the company is healthy for online competition, and that its seemingly substantial grip on search has the potential to erode near-instantaneously should a competing technology emerge.
Google has become more sensitive to antitrust accusations, with CEO Eric Schmidt suggesting during a May 7 Google shareholder meeting that the company would become "more careful about when and how we do things."
In a bid to more effectively challenge Google, Microsoft and Yahoo are rumored to be in talks over a potential search and advertising deal, clearing away any bad blood from Microsoft's failed 2008 takeover attempt in the name of mutual interest.
Microsoft CEO Steve Ballmer and Yahoo CEO Carol Bartz had reportedly been discussing the idea of Yahoo handling Microsoft's display advertising, with Microsoft taking Yahoo's search advertising. Should the companies come to an agreement, however, their combined market share would still remain healthily behind Google's, according to various research firms' 2009 reports.