Google gained 0.4 percent from 47.0 percent to 47.4 percent and the second biggest search engine, Yahoo, increased its marketshare with 0.3 percent to 28.5 percent in December.
Microsoft's MSN search engine lost 0.5 percent marketshare and now has only 10.5 percent of the U.S. search market. Ask.com's share dropped 0.1 percent to 5.4 percent.
The firm estimates web users in the U.S. conducted 6.7 billion searches in December, which is 1 percent more than in November and 30 percent more than December 2005.