Oregon Revised Statutes Public Officers and Employees § 242.768

(1) The appointing power shall make permanent appointments from the list of candidates certified. If any probationer is not discharged during the period of probation, the appointment is permanent.

(2) When there is no candidate upon the entrance register from which a position may be filled, the appointing power may, with the consent of the commission, fill such position by temporary appointment. A temporary appointment shall not continue for more than three months. No classified position shall be filled by a temporary appointment for more than three months in any calendar year.

(3) The commission shall establish rules and regulations under which temporary appointments may be made. Temporary appointments shall be valid only until there are available candidates on the register. No temporary appointment shall be made to fill any position for which a promotional examination is given and an eligible register maintained.