March 24 (Bloomberg) -- Google Inc. shares gained as much as 8 percent, the biggest rise since October, as the world's most-used Internet search engine will be added to the Standard & Poor's 500 Index.

Google replaces Burlington Resources Inc., an oil company being acquired by ConocoPhillips, after the close of trading on March 31. Google, with a fourfold increase in its shares since its initial stock sale, was valued at $101.6 billion yesterday, more than all but 18 members of the index.

``Google has a brand which is synonymous with search,'' said Jordan Rohan, an RBC Capital Markets analyst.

The decision, announced late yesterday, will broaden ownership in Mountain View, California-based Google as managers of funds that use the index as a benchmark purchase shares. Funds with more than $4 trillion track the S&P 500, including about $1.1 trillion in index funds, according to S&P.

The company is picking up market share in search and this month outlined a plan to improve the relevance of its online advertisements and sell spots across all media. In a note titled ``In Google We Trust,'' analyst Scott Devitt at Stifel Nicolaus today raised his rating on the stock to ``buy'' from ``hold''

Google advanced $23.91 to $365.80 in Nasdaq Stock Market trading and reached as high as $370.09. The shares, sold at $85 apiece in its initial public offering in August 2004, had lost 18 percent this year before its inclusion.

``This looked like the right time to do it,'' said David Blitzer, chairman of the S&P's index committee. After the stock ``seemed to almost go straight up'' late last year, ``if we have the opportunity to wait, we usually do take it.''

S&P Adjustment

While Google is the most valuable company ever to join the S&P 500, the stock will only be the second-largest addition because S&P will count just 68 percent of the shares available for trading, according to Nicholas Gulden, an analyst at Citigroup Inc. in New York.

The calculation reflects the fact that Google has a class of stock that doesn't trade. Founders Sergey Brin and Larry Page and Chief Executive Officer Eric Schmidt own most of the shares, which have 10 times as many votes as the publicly traded shares.

After the so-called float adjustment, Google will be behind JDS Uniphase Corp., a maker of fiber-optic equipment that was added in 2000.

S&P 500 fund managers will have to buy $7.3 billion of Google's stock because of its inclusion, Gulden estimated. Index funds will receive $1.7 billion for the Burlington Resources shares they sell. The $5.6 billion difference ``is one of the largest related to a single stock we have ever seen,'' he said.

The stock will become the highest-priced among the index's members, surpassing Goldman Sachs Group Inc., whose shares closed yesterday at $151.67.

`Tighten Up'

The inclusion provided another chance for analysts to call on Google to abandon its policy of not giving quarterly earnings forecasts, often a topic since finance chief George Reyes said on Feb. 28 that growth was slowing. His comments caused the shares to slide.

``For a company that now has the status of being added to the S&P 500, they need to tighten up and do it in a hurry,'' Rohan said. ``They should be offering financial guidance, which will reduce volatility for the shares. The shares will be in a lot of retirement funds. They need to tighten up.''

To contact the reporter on this story: John Melloy in New York at jmelloy@bloomberg.net; Dune Lawrence in New York at dlawrence6@bloomberg.net

Last Updated: March 24, 2006 16:24 EST