Billions at stake: Most expensive divorce ever looms for US oilman

A US court must rule on what may be the most expensive divorce in history, as oil mogul Harold Hamm's wife seeks a share of his US$17 billion (A$18.2 billion) company.

Hamm v. Hamm is in its second week at trial inside a closed Oklahoma City courtroom, NBC News reports.

The legal sticking point is whether Mr Hamm, chief executive of Continental Resources and one of the world's 50 richest people, gained his fortune through luck or hard work.

If his work made him wealthy — a US divorce law concept known as "active appreciation" — then Mr Hamm's company is a martial asset and subject to equitable division.

If his wealth is due to "passive" factors outside his control, such as market forces or the efforts of autonomous managers, then it remains Mr Hamm's personal property.

Mr Hamm founded Continental Resources in 1967, two decades before he married Sue Ann, and his company's value has quintupled in recent years, according to an economic analysis by his wife's legal team.

The Hamms never signed a pre-nuptial agreement.

Ms Hamm, 58, would only need to get about a quarter of Mr. Hamm's net worth to surpass the $4.8 billion judgment reportedly made in May against Russian "fertilizer king" Dmitry Rybolovlev.

The market is anticipating a massive loss for Mr Hamm. The same day his divorce went public last year, his company's share price fell 3 percent after months of gains.

The case is expected to conclude within the next few months.