Google posted a fourth-quarter profit of $US2.71 billion (or $9.50 per share), up from $US2.54 billion in the year-ago quarter.

Revenue increased 25% to $US10.58 billion, or $US8.13 billion after commissions made to partners.

Analysts had expected earnings of $10.49 a share on revenue of $8.41 billion after deducting traffic-acquisition costs, and earnings of $US10.49 a share.

Google does not offer an financial guidance.

The company's shares [NAS:GOOG] fell more than 9% in after hours trading to $US639.57 after rising 6.66% during the regular session.

The stock has a 52-week range of $US432 - $US670.25.

Google's operating expenses climbed from 32% of reveune (from the year-ago quarter's 30%) as the company invested more heavily in data centres and other infrastructure.

Amid the profit climb, there was suprising weakness in the company's core business. Google's average cost-per-click - which represents the prices paid for clicks by advertisers - fell 8% in the fourth quarter. Google blamed the decrease on more clicks on lower-priced ads.