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In this Jan. 17, 2012 photo, a sign for Google is displayed behind the Google android robot, at the National Retail Federation, in New York. Google Inc., releases quarterly financial results Thursday, Jan. 19, 2012, after the market close. (AP Photo/Mark Lennihan)

SAN FRANCISCO - Google's moneymaking machine misfired badly in the fourth quarter as its advertising prices fell during the holiday marketing season.

The results announced Thursday fell way below the lofty expectations of stock market analysts. That caused Google's shares to plunge more than 9 per cent after the numbers were released.

Google Inc. earned $2.7B, or $8.22 per share, during the October-to-December period. That's just a 6 per cent increase from $2.5B, or $7.81 per share, at the same time in 2010.

If not for certain items, Google says it would have earned $9.50 per share. Analysts surveyed by FactSet had expected $10.51 per share.

Revenue climbed 25 per cent from the previous year to nearly $10.6B.

After subtracting ad commissions, Google's revenue totalled $8.1B. That was about $300M below the average analyst forecast.

The disappointing performance stemmed from a surprising downturn in the prices that the Internet search leader collects for each click. The average price declined 8 per cent from the same time in 2010.

The erosion reversed what had been happening earlier in the year. The year-over-year increases in Google's price per ad click had ranged from 5 per cent to 12 per cent increase in the first three quarters of 2010.

The fourth quarter marked the first time Google's revenue surpassed $10B for any three-month period in the company's 13-year history.

Reaching that milestone wasn't enough to impress investors. Google shares shed $58.56 to $581.01 in Thursday's extended trading.