Okla. Stat. tit. 60, § 175.61

Prudent Investor Rule. A. Except as otherwise provided in subsection B of this section, a trustee who invests and manages trust assets owes a duty to the beneficiaries of the trust to comply with the prudent investor rule set forth in the Oklahoma Uniform Prudent Investor Act. B. The prudent investor rule, a default rule, may be expanded, restricted, eliminated, or otherwise altered by the provisions of a trust. A trustee is not liable to a beneficiary to the extent that the trustee acted in reasonable reliance on the provisions of the trust.