Electric power utilities are facing with increasing awareness of environment conditions and very expensive infrastructure investments due to the continually increasing demand for electricity. Demand side management can play a very important role in meeting the challenges faced by power utilities. This paper is mainly focused on the effects of one aspect of the various demand side management measures, which is load shifting, on reliability indices, reliability index probability distributions and peak load carrying capabilities for a bulk electric system. Load forecast uncertainty is an important consideration in an electric power system particularly when there is increased competition in the electric utility industry and more comprehensive risk evaluation is required. The interactive impacts of demand side management programs and the consideration of load forecast uncertainty on system reliability are also investigated.