UPDATE 3-Baidu net aided by Olympics, jumps 91 pct

* Q3 EPS excl options $1.54 vs Reuters Estimates $1.34

* Revenue $135.4 mln vs Reuters Estimates $135.2 mln

* Sees Q4 rev $151-$155 mln, at or above forecast midpoint

* Shares down 2.4 percent after-hours

(Writes through, adds C2C and share buyback paragraphs)

SAN FRANCISCO, Oct 22 (Reuters) - Chinese Internet search leader Baidu Inc (BIDU.O) posted a 91 percent rise in quarterly net profit, after a surge in Web usage tied to the Beijing Olympics, and said it expects continued strong revenue growth.

Baidu shares, however, fell 3.0 percent to $243.50 in extended trade following the report, after closing up slightly to $249.09 on Nasdaq in regular session trading.

The Nasdaq .IXIC finished down 4.77 percent.

Baidu's shares have fallen by about a third over the past five months, in line with general weakness in global markets, raising the possibility the company could be considering a share buyback with its some $340 million cash stockpile.

"We do want to definitely put the cash into the best use," Jennifer Li, the company's chief financial officer, said during a teleconference with analysts. But the company did not have any plans to do so, she added.

Net income rose to $51.2 million in the third quarter from $24.2 million from a year earlier. Net profit per share was $1.47, beating the $1.27 per share forecast by Reuters Estimates.

For the fourth quarter, the company said it expects total revenue ranging from $151 million to $155 million, which would represent growth of 80-85 percent growth over a year ago.

With competition rising in China's fast-growing web market, the world second largest, Baidu was branching out into other areas.

Baidu began developing a new consumer-to-consumer (C2C) platform a year ago, which was beta launched last week, moving into a market dominated by Taobao, an affiliate of Alibaba.com (1688.HK), the country's top e-commerce firm.

The Alibaba group has committed an additional $733 million over the next five years into Taobao, a five-year old free service for buyers and individual sellers that broke even only recently.

"There is competition in the market, but our focus is meeting the information needs of our existing users," said Chief Executive Robin Li.

Baidu was testing the market to judge whether to move more aggressively into C2C, said Robin Li.

Profit excluding employee stock compensation costs rose 95 percent from a year earlier to 364.9 million yuan.

Baidu dominates the Chinese Web search and advertising market, with an estimated two-thirds of the audience in the world's most populous market.

Google Inc (GOOG.O), which is the global market leader in Web search, is a distant No. 2 in China.

Baidu ranks No. 3 worldwide behind Yahoo Inc (YHOO.O), according to data from market research firm comScore, but its customers are largely limited to China.

Baidu's revenue increased 85 percent to 919.1 million yuan from a year earlier, largely in line with analysts' forecasts.

The number of active online marketing customers running Baidu-search advertising grew to 194,000, an increase of 7.2 percent from 181,000 customers in the second quarter.

(1$=6.83 yuan) (Reporting by Eric Auchard in San Francisco and Kirby Chien in Beijing; Editing by Bill Tarrant)