Interest Calculation: Rates and Methodology

The Commission, on a quarterly basis, publishes interest rates for oil, natural gas, and electricity for determination of refund purposes. The interest rates on this page as well as the archived rates are the same for oil, natural gas, and electricity. Please note that the interest rates for oil apply only as far back as 1983.

• Electric Interest Rates are Calculated in Accordance with Section 35.19a of the Commission's regulations. Section 35.19a, subsection (iii)(A) provides that “[t]he applicable average prime rate for each calendar quarter shall be the arithmetic mean, to the nearest one-hundredth of one percent, of the prime rate values published in the Federal Reserve Bulletin, or in the Federal Reserve's “Selected Interest Rates” (Statistical Release H. 15), for the fourth, third, and second months preceding the first month of the calendar quarter.” For example, the refund interest rate for the fourth quarter of a year (October 1 – December 31) would be calculated using the prime rate values published on June 30, July 31 and August 31.
• Gas Interest Rates are Calculated in Accordance with Section 154.501(d) of the Commission's regulations and its predecessors
• Oil Interest Rates are Calculated in Accordance with Section 340.1(c)(2) of the Commission's regulations