In one of the largest U.S. divorce settlements ever, billionaire oil baron Harold Hamm, 68, has been ordered to turn over more than $1 billion in assets and cash to his ex-wife, 58-year-old Sue Ann Hamm. Calling the settlement unfair, Hamm’s ex-wife plans to appeal. The settlement was just 6 percent of the $18 billion increase in the couple’s assets at the time the divorce trial began in August. Hamm is the chief executive officer of Continental Resources and Oklahoma’s richest person.

Oklahoma divorce law typically requires that the “active” growth in wealth, including premarital property, be divided, but only if it resulted from the skill or efforts of either spouse during the marriage. Carolyn Thompson, who is an Oklahoma family law expert, said that the ruling by divorce judge Howard Haralson indicates that most of the increase in assets was due to “passive means,” in other words, to market factors outside Hamm’s control.

However, Hamm’s employees consider him to be a micro-manager, insisting on signing off on everything from new oil wells to petty cash purchases over $500. One passage in Haralson’s ruling states that he had the “ultimate authority” to make decisions on behalf of Continental. The judge rejected the claims of the expert witnesses testifying for Sue Ann Hamm, who told the court that Hamm’s astute management was what resulted in the company’s growth.

During the 26 years of the couple’s marriage, Continental’s value rose to $20 billion, from less than $50 million when they wed. Haralson found that only $1.4 billion of that growth was a result of the skills, efforts or “expended funds” of either spouse. The settlement came after two years of legal negotiations and a two-and-one-half-month trial.