Oregon has no duty to retreat. The use of force for self defense can only be used, when it is reasonably believed that it is needed to prevent immediate harm. This applies to defense of one's self or defense of a third party. The force used for self defense, must be proportional to the believed force that the aggressor would have used.
Deadly force can only be used to defend one's self when it is believed that there is an immediate threat of a forcible felony. Or when the aggressor is "about to use unlawful deadly physical force against a person." ORS 161.219