We consider a generation company operating in the liberalized electricity market, whose production system consists of hydro and thermal plants. Production is sold either directly to customers, by means of bilateral contracts, or on the spot market, where the electricity price is unknow until the market clearing process has taken place. Price risk may be hedged by financial tools provided by the Derivative Electricity Market. In this work futures contracts are considered, i.e. agreements to sell electricity in the future for a specified price. A Mixed Integer Linear Programming model is introduced for determining the unit commitment of thermal units and the dispatchment of available thermal units and hydro plants, aiming at maximizing profits. Numerical results on a case study are reported.