Harold Hamm, 65, and Aubrey McClendon, 51, are two billionaires who made their fortunes in the oil and gas business.

FORBES: Magazine Article

On Friday, Reuters published an exhaustive investigation into the impending divorce of Oklahoma oil mogul Harold Hamm.

FORBES: Oil Billionaire Harold Hamm's Divorce Could Be World's Most Expensive At Over $5 Billion

As big as the Bakken is (oil billionaire Harold Hamm thinks it could hold 24 billion barrels of recoverable oil), the Bazhenov shale of western Siberia is estimated to be 80 times bigger.

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In a fitting lead-in to the July 4th holiday, Continental Resources Chairman and CEO Harold Hamm was one of the biggest billionaire winners on Tuesday after publicly backing a different kind of American independence.

FORBES: Billionaire Harold Hamm Made News, Money Tuesday Backing American Independence

Instead of cutting his teeth in the oilfields like Exxon Mobil CEO Rex Tillerson or wildcatting billionaire Harold Hamm, Watson studied agricultural economics and started his oil career as a financial analyst, not a roughneck.

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Have any thoughts about Harold Hamm?

FORBES: Exclusive: Billionaire Harold Hamm Hits Back Against WSJ Allegations

But Harold Hamm does.

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New pledge signatories announced today include Joyce and Bill Cummings, Ray and Barbara Dalio, John Paul DeJoria, Phillip and Patricia Frost, Harold and Sue Ann Hamm, Vinod and Neeru Khosla, Rich and Nancy Kinder, Edward W. and Deedie Potter Rose, Lynn Schusterman, and Annette and Harold Simmons.

FORBES: Ten More Tycoons Sign Buffett And Gates Giving Pledge: Dalio, Kinder, DeJoria