Ministries of finance are often asked toguarantee a state-owned electricity utility‘s paymentsto an independent power producer under a power-purchaseagreement. To decide whether to grant the guarantee, theministry should have at least a rough estimate of theguarantee‘s expected cost. Making use of an analogybetween a power-purchase agreement and a debt contract, thispaper shows how the ministry can get such an estimate byapplying a method developed to estimate the expected cost ofdebt guarantees. An estimate of the probability of theutility‘s not being able to meet its obligations underthe power-purchase agreement can be derived from theutility‘s actual or estimated credit rating in theabsence of government support. The government‘sexpected payments under the guarantee can then be estimatedby multiplying the utility‘s payments under thepower-purchase agreement by this probability. The estimatesproduced by the method will be imprecise, but the method maybe easier to apply than alternative methods, and animprecise estimate may be better for policy makers than no estimate.