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 to the size of the US 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 US economy.

The survey in the magazine's October 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 charitablecontributions.

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 JP 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.