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 John D. Rockefeller, Andrew Carnegie, Cornelius Vanderbilt and John Jacob Astor amassed far greater wealth when compared to the size of the U.S. economy of their time.The survey in the magazine's Oct. 12 issue found that Gates' $62 billion makes up a far smaller share of today's economy than Rockefeller's wealth 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 his-tory: Carnegie's steel, Vanderbilt's railroads and Astor's real estate.

Gates is one of only three Americans on the list who are still alive, along with investor Warren Buffett at No. 13 and fellow Micro-soft 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.