Oregon Revised Statutes Property Rights and Transactions § 91.070

One who holds the lands or tenements of another, under the demise of the other, and no certain time has been mentioned, but a monthly rental has been reserved, is considered a tenant from month to month. Except as otherwise provided by statute or agreement, such tenancy may only be terminated by either the landlord or tenant giving the other, at any time during the tenancy, not less than 30 days' notice in writing prior to the date designated in the notice for the termination of the tenancy. The tenancy shall terminate on the date designated and without regard to the expiration of the period for which, by the terms of the tenancy and holding, rents are to be paid.