Customer interruption costs due to failure in electrical energy supply depend on many factors. A procedure is developed to estimate the customer outage costs on a distribution feeder subjected to a specific outage event. The data required to perform a detailed evaluation is illustrated and discussed, including the customer composition on the feeder, the customer demand profiles at the feeder load points and the relevant customer damage functions. The procedure presented in the paper is illustrated by application to a specific distribution feeder in the city of Saskatoon. The customer costs associated with power supply failures are a function of the time of day, day of the week and time of year. They are also strongly influenced by the duration of the outage event. The effect of outage duration and the time of outage occurrence is illustrated.