Obligatory reinsurance contract in which a reinsurer agrees to pay for all or a large portion of losses up to a limit, when these losses exceed the retention level of the cedent. The reinsurance premium paid by the cedent is calculated independently of the premium charged to the insured. It is not expected that every treaty will pay for itself or that every loss will be recouped by the reinsurer. When a cedent reinsures on a nonproportional basis, it retains substantially more of its profits than reinsuring on a proportional basis. Nonproportional differs from proportional reinsurance in that it does not involve the sharing of risks.