Oregon Revised Statutes Insurance § 742.534

(1) Except as provided in ORS 742.544, every authorized motor vehicle liability insurer whose insured is or would be held legally liable for damages for injuries sustained in a motor vehicle accident by a person for whom personal injury protection benefits have been furnished by another such insurer, or for whom benefits have been furnished by an authorized health insurer, shall reimburse such other insurer for the benefits it has so furnished if it has requested such reimbursement, has not given notice as provided in ORS 742.536 that it elects recovery by lien in accordance with that section and is entitled to reimbursement under this section by the terms of its policy.  Reimbursement under this subsection, together with the amount paid to injured persons by the liability insurer, shall not exceed the limits of the policy issued by the insurer.

(2) In calculating such reimbursement, the amount of benefits so furnished shall be diminished in proportion to the amount of negligence attributable to the person for whom benefits have been so furnished, and the reimbursement shall not exceed the amount of damages legally recoverable by the person.

(3) Disputes between insurers as to such issues of liability and the amount of reimbursement required by this section shall be decided by arbitration.

(4) Findings and awards made in such an arbitration proceeding are not admissible in any action at law or suit in equity.

(5) If an insurer does not request reimbursement under this section for recovery of personal injury protection payments, then the insurer may only recover personal injury protection payments under the provisions of ORS 742.536 or 742.538.