US oilman Harold Hamm to pay ex-wife nearly $1 billion in divorce settlement
US billionaire Harold Hamm and his then wife Sue Ann at the TIME 100 Gala in New York, on April 24, 2012 (AFP Photo/Jemal Countess)

Multibillionaire American oilman Harold Hamm has been ordered to pay almost $1 billion to his ex-wife to settle one of the most expensive divorce cases in US history.

According to a ruling filed in Oklahoma on Monday, the CEO of Continental Resources owes his former wife Sue Ann Hamm $995,481,842 for "property division alimony."

Hamm, 68, is one of America's richest people. His 68-percent stake in Continental Resources is worth nearly $14 billion, according to Forbes.

Time magazine included him in its 2012 list of the 100 most influential people, noting how he had grown his business through the use of hydraulic fracturing (fracking).

The couple were married in 1988.

Hamm must pay Sue Ann, 58, nearly $323 million by the end of the year, then the rest must be paid off in monthly installments of at least $7 million, plus interest. He had already paid her more than $22 million.

The ruling is subject to appeal.