DETROIT (Bloomberg) — It took 51 years for General Motors Co. to go from the largest company on the Standard & Poor's 500 Index to being dropped after its bankruptcy last year. The automaker may need at least another year until it returns.

Initial public offerings "should be seasoned for six to 12 months before being considered for addition to an index", according to methodology listed on S&P's website. A company's inclusion is decided by S&P's US Index Committee.

"We like one year typically that the issue be out and public, trading, to show liquidity, and one year of positive GAAP earnings," Howard Silverblatt, senior index analyst at S&P in New York, said in an interview. GAAP refers to generally accepted accounting principles.

GM, 61 percent owned by the US Treasury Department, said it will sell 365 million shares at $26 to $29 each. The offering seeks to raise as much as $10.6 billion and reduce the US government to a minority shareholder. The Detroit-based automaker will also offer about $3 billion of preferred shares that later will become common stock.

General Motors Corp. was removed from the S&P 500 when it filed for bankruptcy protection in June 2009 after posting $88 billion of losses since 2004. General Motors Co. emerged 39 days later.

The last time GM was the largest company on the S&P 500 by market value was November 1958, at $13.5 billion, Silverblatt said. GM traded the top spot throughout the 1950s with AT&T Inc.

Ed Whitacre, who will retire as GM's chairman at the end of the year, was chairman and chief executive officer of the Dallas-based telephone service provider until 2007.

At the IPO's midpoint price of $27.50 each, GM would have a market capitalization of $41.25 billion, based on 1.5 billion shares that will be outstanding after the offering, according to the company's filing and data compiled by Bloomberg.

GM said separately yesterday that it had third-quarter net income attributable to common stockholders of $1.9 billion to $2.1 billion. The results are preliminary, and details are scheduled to be released Nov. 10, GM said in a statement.

The company had earnings before interest and taxes of $2.2 billion to $2.4 billion on revenue of about $34 billion for the three months ended Sept. 30, according to the statement. GM earned $2.6 billion in the first half of the year.

S&P has made exceptions to the addition guidelines, including that companies post a year of positive earnings, Silverblatt said. Warren Buffett's Berkshire Hathaway Inc. reported a $1.53 billion first-quarter loss last year and was picked to join the S&P 500 on January 26.

"We looked at other criteria and stated that, yes, there was a negative item that they had in there at one point for earnings within the last year," Silverblatt said. "However, looking at the balance sheet and using the whole methodology, it was acceptable."