Oregon Revised Statutes Elections § 250.315

(1) An initiative or referendum petition relating to a city measure shall be filed with the city elections officer for signature verification. The filed petition shall contain only original signatures.

(2) An initiative or referendum petition relating to a city measure shall not be accepted for filing if it contains less than 100 percent of the required number of signatures.

(3) For any petition requiring a number of signatures exceeding 4,500, the Secretary of State by rule shall designate a statistical sampling technique to verify whether a petition contains the required number of signatures of electors. A petition may not be rejected for the reason that it contains less than the required number of signatures unless two separate sampling processes both establish that the petition lacks the required number of signatures. The second sampling must contain a larger number of signatures than the first sampling.

(4) The Secretary of State may employ professional assistance to determine the sampling technique referred to in subsection (3) of this section.