Despite some market concerns over Google's growth potential in a slowing economy, the search giant continues to report strong growth, with fourth-quarter revenue up 51 percent over the same period the year before.

Google reported revenue of $4.83 billion for the quarter ending Dec. 31 using GAAP (generally accepted accounting principles). Net income for the period was $1.21 billion, compared to $1.01 billion in the third quarter of 2007.

With earnings per share of $4.43, Google just missed analyst consensus of $4.44 on a non-GAAP basis, as polled by First Call.

Google continues to increase revenue from outside the United States, reporting that 48 percent of total revenue in the quarter came from international markets. That's up from 44 percent in the same period a year earlier but the same as the third-quarter 2007.

"The international market is still very nascent with tremendous potential with what we can do," said Eric Schmidt, CEO and chairman of Google, during a conference call to discuss the earnings.

YouTube, the online video site that Google bought in 2006, continues to see strong growth in the United States and around the world, executives said. It is now available in 17 languages, including eight that were added last year.

In conjunction with CNN, YouTube recently offered video of a presidential candidate debate. Almost as many people watched the video on YouTube as on CNN, said Sergey Brin, co-founder and president of technology for Google. "We consider this a great milestone," he said. Google hopes to work on similar partnerships to help grow the YouTube audience in the future, he said.

Despite several bright spots, Google also hit a speed bump during the quarter. "We're still learning how to monetize social networking," said George Reyes, Google's CFO.

Last year Google launched OpenSocial, a development platform for social-networking applications. While it now has 20 partners, Google is disappointed with the money it was able to generate from the platform in the fourth quarter, said Larry Page, co-founder and president of products for Google. "But we're optimistic about the future," he said.

The executives highlighted Google's newer mobile initiatives. Phones running Google's Android operating system are expected later this year. Schmidt was reluctant to estimate the proportion of searches that will come from mobile phones in the near future, but he said he expects that in 10 or 20 years, the majority of searches will be done on mobile phones.

Even though phones running Android will compete with Apple's iPhone, Schmidt, who holds a seat on Apple's board, sees the iPhone as a trailblazer. "The iPhone is the first of a whole generation of products that will be much more search-intensive," he said.

The executives didn't expect a decline in Google's fortunes because of the potential economic slowdown in the United States. "We have not yet seen any negative impact from the rumors of a future recession," said Schmidt. "So we'll see what happens."

Even if the economy does slow, Google is well positioned to keep performing well, said Jonathan Rosenberg, senior vice president of product management and marketing. If more people turn to the Web to look for bargains and comparison shop, that's good news for Google, he said. However, if overall commerce decreases, that could reduce demand for Google's offerings, he said.

This story was updated on Jan. 31, 2008.