Yesterday, comScore released December U.S. search engine rankings. Overall, the U.S. search market grew 1% in December compared to November, as Americans conducted 6.7 billion searches. This still implies a strong 30% annual growth rate.

Interestingly, both Google Inc. (NASDAQ:GOOG) and Yahoo! Inc. (NASDAQ:YHOO) gained market share. At whose expense? Microsoft Corp. (NASDAQ:MSFT), IAC/InterActiveCorp's (NASDAQ:IACI) Ask.com and Time Warner Inc.'s (NASDAQ:TWX) AOL.

Google held 47.3% of the search market, a 0.4% gain from November, which means it served 3.2 billion queries. Yahoo! gained 0.3% to hold 28.5% of the market. Yahoo! served 1.9 billion queries. Microsoft lost 0.5% of its share in search market in December to 10.5%, Ask held 5.4%, down 0.1% and AOL was declined 0.2% to 4.9%.

While Google gaining market share isn't surprising -- the search giant has gained market share in the past 16 of 17 months -- Yahoo!'s gain is encouraging. Yahoo!'s search market share has been stumbling, with Google and Ask.com usually the ones gaining. With Yahoo!'s new search advertising platform, Panama, will this share gain (and hopefully the next ones), also translate into better monetization and higher revenue?