(FUELFIX) — For the past six years, Elaine Tettemer Marshall, the fourth-richest woman in the U.S., has avoided the spotlight that ordinarily accompanies great wealth.

The 70-year-old Dallas resident controls almost 15 percent of Koch Industries Inc., the second-largest closely held company in the U.S. Her stake in the Wichita, Kansas-based industrial conglomerate, which generates annual sales of $110 billion, is worth more than $12.7 billion, according to the Bloomberg Billionaires Index, which has expanded to 100 names. The only American women richer are Wal-Mart Stores Inc. (WMT) heiresses Alice and Christy Walton, and 71-year-old candy scion Jacqueline Mars.

Marshall, who gained control of the Koch stake following the death of her husband, E. Pierce Marshall, in 2006, has never appeared on an international wealth ranking, although her estate has been at the center of two U.S. Supreme Court cases involving her mother-in-law, Anna Nicole Smith.

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