Microsoft and Google each grabbed a tiny sliver more of the U.S. search market last month, according to ComScore.

Both companies gained three-tenths of a point of market share in March, compared with February.

Overall, Google sites accounted for 65.7 percent of the 16.9 billion searches in the U.S. last month, ComScore said yesterday. Microsoft sites snagged 13.9 percent, while Yahoo sites held 15.7 percent. As always, ComScore's figures specifically track "explicit core" searches, which are search terms that people manually enter on a Web page.

Beyond the core search numbers, Google's and Microsoft's "powered-by" figures show a bigger piece of the puzzle.

Combining the searches done on Google sites with the Google-powered searches on AOL and the Ask Network, Google held 68.2 percent of the market in March, compared with 68 percent in February.

For Microsoft, combining Bing searches on its own sites with its Bing-powered searches on Yahoo, Microsoft accounted for 26.4 percent of market share last month, versus 26.2 percent in February. (According to ComScore, Google doesn't account for all searches on AOL or Ask, and Microsoft doesn't run every search on Yahoo. Some searches are internal, such as those within e-mail.)

Using that calculation, Google and Microsoft together accounted for 94.6 percent of all searches done in the U.S. last month.

ComScore's powered-by numbers are slightly off from those released by Experian Hitwise this week, which pegged Microsoft's share at 30 percent and Google's at 64.4 percent.