Mont. Code Ann. § 1-6-102

An oath or affirmation in an action or proceeding may be administered by the person who swears or affirms expressing that person's assent when addressed with "You do solemnly swear (or affirm, as the case may be) that the evidence you will give in this issue (or matter), pending between.... and...., is the truth, the whole truth, and nothing but the truth, so help you God".