Google's shares fell 10 percent in after hours trading on Thursday after the Internet search giant missed Wall Street's revenue targets.
Google's net revenue, which excludes fees shared with partner websites, was $8.13 billion in the fourth quarter, versus $6.37 billion in the year-ago period. Analysts polled by Thomson Reuters I/B/E/S were looking for net revenue of $8.4 billion.
The revenue shortfall represents a rare miss for Google, which has exceeded Wall Street's revenue targets for the past 8 consecutive quarters.
The amount of clicks on Google's search ads increased sharply during the last three months of the year, but the cost per clicks - the amount of money that Google charges advertisers for the ads - decreased 8 percent from the third quarter and 8 percent from the year ago period.
Google's operating expenses increased to 32 percent of revenue during the fourth quarter, versus 30 percent of revenue at this time last year.
Google said on Thursday that it earned $2.71 billion, or $8.22 per share in the fourth quarter, compared to $2.54 billion, or $7.81 per share in the year-ago period.
Excluding certain items, Google said it earned $9.50 per share.