An electric power outage, which has many social and most importantly economical outcomes, is an undesired and unpleasant event that leads to inevitable damages to the society. Regardless of its psychological effects, preventing power outages presents a vital importance due to its severe effects on economy. Therefore, since it has so many motivating factors, studying and estimating the outage costs have been an attractive and popular field of study for the recent years. The electric supply utilities want to know the customer interruption costs for planning and investment purposes. Official departments want to know it for legislation and applying fine reasons. And of course, the customers desire to find out their true interruption costs to see their real losses to implement precautions in order to prevent such damages. These facts clearly show the meaning and the importance of evaluating power outage costs. This work is an attempt to estimate these costs on an objective manner by taking Finland's industry and service sectors as proper case studies.