Google shares for the online advertising market increased by 23.7 percent, less than 24.2 percent in the third quarter making the firm's first decline in two years.
Google lead the overall Internet advertising market by a factor of about 1.5, and a factor of two against Yahoo.
The decline of the firm's share was as a result of Google's quarter-to-quarter revenue growing by less than the overall market, 11.8 percent versus 14.1 percent respectively.
Google's market share grew by 2.1 percent as compared with the same quarter in 2006.
Google lead the overall market growth of 27.5 percent after its sales increased by 40.2 percent in the fourth quarter of 2007 compared with 2006, to $1,726 billion.
After the rejection of the take-over bid from Microsoft, Yahoo underperformed in the overall market when its shares declined to 11.4 percent in the quarter from 12 percent last year.
Yahoo's revenue growth rates continued to increase steadily from a low of 2.1 percent in the first quarter of 2007 and its revenue growth continued to improve, increasing by 21.7 percent over the fourth quarter of 2006 to $832 million.
Microsoft settled in the third place of the advertisement market at about half the size of Yahoo.
Microsoft's U.S. online advertising revenues grew by 23.6 percent from last year, to $411 million although its market share fell to 5.6 percent from 5.8 percent.