Oregon Revised Statutes Elections § 260.156

(1) The Secretary of State may adopt rules for the manner of determining and reporting expenditures and contributions under this chapter, including but not limited to rules for allocation of contributions and expenditures and for determination of fair market value of contributions other than money. Rules adopted under this section shall provide for proportional reporting of expenditures and contributions that benefit more than one candidate or political committee.

(2) The valuation or allocation of any contribution or expenditure under a rule adopted by the Secretary of State before the contribution or expenditure was made or, if it is a continuing contribution or expenditure, the valuation or allocation of that part available to and used on behalf of the candidate after the adoption of the rule, shall be presumed to be the fair market value or allocation of it.