Microsoft Chairman Bill Gates may be the richest American now, but a new study finds that Gates ranks only No. 5 on the list of the richest men throughout U.S. history.

The survey by American Heritage, a magazine published by Forbes Inc., found that the great titans of American industry - John D. Rockefeller, Andrew Carnegie, Cornelius Vanderbilt and John Jacob Astor - had amassed far greater wealth when compared with the size of the U.S. economy of their time.Sure, Gates' fortune of $62 billion looks pretty good now. But while fortunes have been growing larger over time, so has the overall size of the U.S. economy.

The survey in the magazine's Oct. 12 issue found that Gates' holdings are a far smaller share of today's economy than Rockefeller's was at the time of his death in 1937.

Adjusting for the tremendous growth in America's economy since then, the survey found that Rockefeller's wealth would be worth a whopping $190 billion today, including all of his charitable contributions.

In addition to Rockefeller's oil, other key industries were also represented on the list of the 40 richest Americans throughout history: Carnegie's steel, Vanderbilt's railroads and Astor's real estate.

Gates should still feel lucky, though - he's one of only three Americans on the list who are still alive today, along with superstar investor Warren Buffett at No. 13 and fellow Microsoft bigwig Paul G. Allen at No. 22. Wal-Mart founder Sam Walton, No. 11, died in 1992.

The list includes other well-known financiers and industrialists such as banker J.P. Morgan and automaker Henry Ford. But it also includes some figures who are lesser-known today, such as sewing machine king Edward Clark and sugar magnate Claus Spreckels.

The study by Michael Klepper and Robert Gunther grew out of research the two did for a 1996 book "The Wealthy 100: From Benjamin Franklin to Bill Gates - A Ranking of the Richest Americans, Past and Present." The authors updated their data for the magazine article.

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ADDITIONAL INFORMATION

The 10 richest Americans

A ranking of the 10 richest Americans of all time, compiled by American Heritage magazine, published by Forbes Inc. The conversions were made using a formula comparing the orginal value of wealth with the size of the U.S. economy at the time. The rankings appear in the magazine's Oct. 12 issue.

Name Value of wealth

John D. Rockefeller $189.6 billion

Andrew Carnegie $100.5 billion

Cornelius Vanderbilt $95.9 billion

John Jacob Astor $78 billion

William H. Gates III $61.7 billion

Stephen Girard $55.6 billion

A.T. Stewart $46.9 billion

Frederick Weyerhaeuser $43.2 billion

Jay Gould $42.1 billion

Marshall Field $40.7 billion