THE OKLAHOMA BAR JOURNAL 16 | JANUARY 2026 Statements or opinions expressed in the Oklahoma Bar Journal are those of the authors and do not necessarily reflect those of the Oklahoma Bar Association, its officers, Board of Governors, Board of Editors or staff. Family Law Thirty Years of Thielenhaus: The Dubious Origins of That Case’s Burden of Proof Requirement By Ryan J. Reaves In Thielenhaus, the late Justice Marion Opala synthesized existing case law to create a clear and ostensibly workable rule governing the division of premarital property that has increased in value during the marriage: Where, as here, a spouse brings separate property to the marriage, its increased or enhanced value, produced by investment managed by neither spouse or by appreciation, inflation, changing economic conditions, or circumstances beyond the parties’ control, cannot be treated as a divisible marital asset unless, of course, there be proof that the increase resulted from efforts, skills or funds of either spouse. The non-owning spouse’s interest in the increased separate estate of the other, when established through efforts, skills or expended funds, stands confined to the enhanced value of that separate property.2 The rule set forth in Thielenhaus was largely a combination of the rules set out in Templeton v. Templeton,3 Moyers v. Moyers4 and May v. May.5 In that sense, it was largely a restatement of existing law. However, the Thielenhaus opinion included a far more significant departure from existing law when it advised, “The burden is upon the non-owning spouse to show that the enhancement is the result of either spouse’s endeavors.”6 Further, Thielenhaus held that this burden of proof extended to the “three critical value-assessment elements,” which are: 1) the value at the date of marriage, 2) the increase in value due to market forces and 3) the increase in value related to the funds, skills and efforts of the parties.7 This, in effect, created a presumption that the increase in the value of separate property during marriage is separate property. Since this rule was pronounced 30 years ago, it has become the foundation of Oklahoma’s law on in-marriage enhancement of separate assets. However, placing the burden of proof in a manner designed to protect the separate estate from marital claims is highly unusual. Oklahoma marital property law contains a number of evidentiary presumptions, and virtually every one of those supports the acquisition of marital property rather than the protection of separate property.8 Oklahoma law presumes that THERE ARE FEW, IF ANY, CASES IN OKLAHOMA FAMILY LAW more frequently cited than Thielenhaus v. Thielenhaus.1 This decision was published (as modified) on Sept. 1, 1995 – just over 30 years ago. While Thielenhaus may be cited for a great many issues, its central and most enduring holding is the one related to in-marriage enhancement of a separate asset. After 30 years, it seemed only fitting to take a fresh look at Thielenhaus and consider whether there might be a need for a different approach.
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