Oregon Revised Statutes Revenue and Taxation § 305.150

(1) The Department of Revenue is authorized to enter into an agreement in writing with any person relating to the liability of such person, or of the person or estate for whom the person acts, for any taxable period open to adjustment under the pertinent statutes of limitation, in respect of any revenue measure which the department is required to administer.

(2) Such agreement shall be final and conclusive on the date agreed to, and, except upon a showing of fraud or malfeasance or misrepresentation of a material fact, the question, issue or case shall not be reopened as to the matters agreed upon, and, in any action, suit or proceeding, such agreement, or any determination, assessment, collection, refund, abatement or credit made in accordance therewith shall not be annulled, modified, set aside or disregarded.