Oregon Revised Statutes Property Rights and Transactions § 90.370

(1)(a) In an action for possession based upon nonpayment of the rent or in an action for rent when the tenant is in possession, the tenant may counterclaim for any amount, not in excess of the jurisdictional limits of the court in which the action is brought, that the tenant may recover under the rental agreement or this chapter, provided that the tenant must prove that prior to the filing of the landlord's action the landlord reasonably had or should have had knowledge or had received actual notice of the facts that constitute the tenant's counterclaim.

(b) In the event the tenant counterclaims, the court at the landlord's or tenant's request may order the tenant to pay into court all or part of the rent accrued and thereafter accruing, and shall determine the amount due to each party.  The party to whom a net amount is owed shall be paid first from the money paid into court, and shall be paid the balance by the other party.  The court may at any time release money paid into court to either party if the parties agree or if the court finds such party to be entitled to the sum so released.  If no rent remains due after application of this section and unless otherwise agreed between the parties, a judgment shall be entered for the tenant in the action for possession.