More than $17 billion of Oklahoma oilman Harold Hamm's fortune could be subject to division with his estranged wife, according to an economic analysis presented in their divorce trial, defining the stakes in one of the biggest battles ever over a marital estate.

The analysis of Kenneth Button, an expert witness hired by Sue Ann Hamm, was laid out in court testimony and in a document provided to Reuters by Oklahoma County Judge Howard Haralson. It is one of the first pieces of financial testimony to be released from the trial, which has been conducted mostly in secrecy.

In an uncommon step for a divorce case, Haralson has barred the public from the courtroom on most days and sealed most of the evidence. He says he is trying to protect shareholders in Hamm's Continental Resources from the release of confidential business information. Through his 68 percent stake in Continental, a leading driller in North Dakota, Harold Hamm is believed to own the most oil in the ground of any American.