This paper describes a probabilistic approach for determining the portion of Non-Utility Generation capacity, (NUG "Credit"). that can be relied on as a fimi resource when assessing the adequacy of the Ontario Hydro customer delivery system. The proposed method is based on the criterion that the reliability of supply to the customers on the delivery system should not be affected by the addition of a NUG to that system. Calculations to determine the reliability level consider the system load profile, system contingencies, the load forecast and its uncextainty, the NUG size and the NUG forced outage rate as well as the uncertainty of the in-service date of new facilities. Sensitivity studies are conducted to determine the factors that largely affect the NUG credit. The paper also presents an approximate method for estimating the NUG credit. The method is simple and easy to apply and does not require the detailed calculations of the exact method. A comparison of the exact and approximate methods is illustrated using some numerical examples.