This paper assesses the impact of electricity outages on firms' productivity in Senegal, using cost technical and allocative efficiency scores. Results based on survey data from 528 businesses indicate that power outage duration has a positive significant effect on cost and technical efficiencies, and SMEs were more successful in doing so than larger ones. Further, power outages' frequency, duration and their perceived severity have negative effects on scale efficiency. Finding a solution to the power outage issue while affecting negatively cost efficiency, seems to promote technical and scale efficiencies. Further, having a loans and/or a credit line appeared to have positive effects on technical and scale efficiencies.