ORS § 308.555
The Department of Revenue, for the purpose of arriving at the assessed value of the property assessable by it, may value the entire property, both within and without the State of Oregon, as a unit. If it values the entire property as a unit, either within or without the State of Oregon, or both, the department shall make deductions of the property of the company situated outside the state, and not connected directly with the business thereof, as may be just, to the end that the fair proportion of the property of the company in this state may be ascertained. If the department values the entire property within the State of Oregon as a unit, it shall make deductions of the property of the company situated in Oregon, and assessed by the county assessors, to an amount that shall be just. For that purpose the county assessors shall, if the department so requests, certify to the department the assessed value of the property of the companies assessable by them, but such certification of assessed value is intended to be advisory only and is not conclusive upon the department.
ORS 308.555