Oregon Revised Statutes Cities § 225.270

When any city which owns or operates a municipal electric power plant or system or distributing system, has paid principal and interest to date on all indebtedness incurred in connection therewith, and has created and accumulated an adequate depreciation and replacement reserve in the judgment of the officer having control of such plant or system, the city shall, for the purpose of reducing general property taxes within such city, pay to itself not less than three percent of the annual gross operating revenue of such plant or system, or a volumetric charge based upon the amounts of electricity delivered, transmitted or distributed to retail electricity consumers regardless of the source. The volumetric charge shall not be less than the equivalent of three percent of the gross operating revenues of the municipality utility in 1999. The city shall adjust a volumetric charge to end users such that charges established for different customer classes bear the same approximate relationship as the gross revenues per kilowatt hour paid by the classes in 1999.