The ex-wife of Continental Resources CEO Harold Hamm, Sue Ann Hamm, who was awarded cash and assets worth more than $1 billion in the couple’s divorce this week, plans to appeal the judgment on grounds that it grossly undervalues the marital wealth she is entitled to.

Feeling shortchanged by a ruling that allows Harold Hamm to keep around 94% of the estimated $18 billion rise in his Continental shares during a 26-year marriage, Sue Ann Hamm will appeal within a few weeks, one of her lawyers, Ron Barber, told Reuters on November 13.

Sue Ann Hamm believes the decision was “not equitable”, Ron Barber said.

On November 10, Oklahoma County Court Judge Howard Haralson ordered Harold Hamm, who is believed to own more oil than any other American, to pay his ex-wife $995 million. The ruling allows Sue Ann Hamm to keep additional assets, including a California ranch and an Oklahoma home, worth tens of millions more.

The Hamm v. Hamm divorce judgment is one of the largest in U.S. history, but Sue Ann Hamm’s award is a small fraction of the wealth Judge Howard Haralson allowed Harold Hamm to keep.

Harold Hamm holds more than 68%of Continental’s stock, a stake valued at around $13.5 billion today. It was worth more than $18 billion before the 9 1/2-week divorce trial began in August. Continental shares have fallen sharply since then, in line with global oil prices.

Judge Howard Haralson ruled that $1.4 billion of the growth in his Continental shares during the marriage was “marital capital” to be split with Sue Ann Hamm. The rest was awarded to Harold Hamm as “separate property”.

A lawyer and economist, Sue Ann Hamm worked at Continental during stretches of the couple’s marriage, which began in 1988. At one point, the ruling says, she was an executive in charge of Continental’s crude marketing division. She left the company in 2008. At other times she worked in the home, helping to raise the couple’s two children.

In Oklahoma, a divorce appeal can be heard by a State Court of Appeals panel or the Oklahoma Supreme Court.

A higher court could review the case and affirm Judge Howard Haralson’s judgment, or modify the award. It could also send the case back to Judge Howard Haralson to be re-tried.

Family law experts say the process could take anywhere from 18 months to several years. Sue Ann Hamm has 30 days from when the ruling was filed, on November 10, to appeal it.

As part of the ruling, Judge Howard Haralson ordered Harold Hamm to pay his ex-wife more than $322 million by December 31, and continue with monthly payments of at least $7 million until he covers an additional $650 million balance. She has received around $23 million from the marital estate since filing for divorce in 2012.

To secure the judgment, Judge Howard Haralson placed a lien on 20 million shares of the CEO’s Continental stock. Whether an appeal would alter the payment schedule remains unclear.

Harold Hamm’s attorney, Craig Box, said the CEO considers Judge Howard Haralson’s ruling to be “fair and equitable.” Hamm declined to comment on the prospect on an appeal.

Following the news, shares of Continental extended earlier losses. They fell 3.1% on the day as US oil prices sank below $80 per barrel for the first time in four years.

The Hamms had no prenuptial agreement. During their marriage, Continental’s value soared by around 400-fold, and Harold Hamm, the 13th child of sharecroppers, became Oklahoma’s richest person.

Harold Hamm, now 68, founded Continental in 1967, more than two decades before he married Sue Ann. But Oklahoma law typically requires that the enhanced value of premarital property be split “equitably” in a divorce if it resulted from the efforts or skills of either spouse during marriage.