In this paper, we describe a method for the energy management, according to minimal costs criteria over one year (month after month), of an electrical utility, which has to deal with nuclear and hydro power plants, sale/purchase and exchange contracts, and spot market business. The chosen method for minimizing the costs is linear programming with most variables continuous, and a few binary ones. The results obtained allow us the management of every power plant, contract and the spot market business, in order to respect the economic, physical and environmental constraints.