Oregon Legal Research Blog
Line of succession is governed by the Oregon Constitution. (Note: Oregon does not have a Lieutenant Governor.)
See also Wikipedia and Ballotpedia (and this one) and Secretary of State on succession of the Oregon Governor.
Oregon Constitution Article V (or read the entire Oregon Constitution and early Oregon Constitutions):
“Section 8. Vacancy in office of Governor. [Constitution of 1859; Amendment proposed by S.J.R. 10, 1920 (s.s.), and adopted by the people May 21, 1920; Amendment proposed by S.J.R. 8, 1945, and adopted by the people Nov. 5, 1946; Repeal proposed by initiative petition filed July 7, 1972, and adopted by the people Nov. 7, 1972 (present section 8a of this Article adopted in lieu of this section)]
Section 8a. Vacancy in office of Governor. In case of the removal from office of the Governor, or of his death, resignation, or disability to discharge the duties of his office as prescribed by law, the Secretary of State; or if there be none, or in case of his removal from office, death, resignation, or disability to discharge the duties of his office as prescribed by law, then the State Treasurer; or if there be none, or in case of his removal from office, death, resignation, or disability to discharge the duties of his office as prescribed by law, then the President of the Senate; or if there be none, or in case of his removal from office, death, resignation, or disability to discharge the duties of his office as prescribed by law, then the Speaker of the House of Representatives, shall become Governor until the disability be removed, or a Governor be elected at the next general biennial election. The Governor elected to fill the vacancy shall hold office for the unexpired term of the outgoing Governor.
The Secretary of State or the State Treasurer shall appoint a person to fill his office until the election of a Governor, at which time the office so filled by appointment shall be filled by election; or, in the event of a disability of the Governor, to be Acting Secretary of State or Acting State Treasurer until the disability be removed. The person so appointed shall not be eligible to succeed to the office of Governor by automatic succession under this section during the term of his appointment. [Created through initiative petition filed July 7, 1972, and adopted by the people Nov. 7, 1972 (this section adopted in lieu of former section 8 of this Article)]”