Mont. Code Ann. § 85-1-511

A determination of the rates and terms under which the power must be purchased shall be made by the public service commission upon petition of the facility operator or a public utility or electric cooperative or during a rate proceeding involving the review of rates paid for electricity purchased from the facility. The commission shall render a decision within 120 days from receipt of the petition or before the completion of the rate review proceeding. The rate and terms of the determination must be according to the standards specified in 85-1-512.