(1) The proportional shares of tortfeasors in the entire liability shall be based upon their relative degrees of fault or responsibility. In contribution actions arising out of liability under ORS § 31.600, the proportional share of a tortfeasor in the entire liability shall be based upon the tortfeasor’s percentage of the common negligence of all tortfeasors.

(2) If equity requires, the collective liability of some as a group shall constitute a single share. Principles of equity applicable to contribution generally shall apply. [Formerly 18.445]