ORS 91.050: Tenancy at will.

One who enters into the possession of real estate with the consent of the owners, under circumstances not showing an intention to create a freehold interest, is considered a tenant at will. When the rent reserved in the lease at will is payable at periods of less than three months, a notice to terminate the tenancy is sufficient if it is equal to the interval between the times of payment of rent. The notice to terminate a tenancy at will is sufficient if given for the prescribed period prior to the expiration of the period for which, by the terms of the lease and holding, rents are to be paid.