The objective of this study is to develop mathematical models that meet the finished products requirements at a minimum cost of energy used in the process subject to different operational constraints. An energy-intensive process is chosen for the study.Four different linear programming models are developed. Model 1 is the base form of the other models and focuses on minimizing total energy costs and meeting customer demands subject to operational constraints of the process. In model 2, 3 and 4, constraints of model 1 are adapted to different production and marketing circumstances.Model 2 focuses on reducing inventory-holding costs. Model 3 focuses on utilizing time capacity 100 %. Model 4 focuses on increasing production for more products also taking into account marketing circumstances. Sensitivity analysis of the models yields a better insight to the real problem and gives an idea what is now, and will be in the near future. Since the aim of the thesis is to focus on the energy costs, sensitivity analysis is related to the changes in prices of the resources and their effects on optimal production values.