This article presents a MATLABÀGeneral Algebraic Modeling System (GAMS) combined tool designed to define the optimal power bid to be submitted by generating agents in wholesale electricity markets. This computer application, called OPTIOFER, fits together the best GAMS and MATLAB features for the optimization of hydraulic and thermal generation bids models and their friendly visual representation. OPTIOFER makes use of GAMS to formulate and solve hydro and thermal models, whereas MATLAB and its toolbox GUIDE are used for implementation and graphical representation. The motivation for developing the package is to provide a flexible simulation environment for ongoing research conducted at the Electrical Engineering Department of Carlos III University, Madrid, Spain, and to enhance, mainly, graduate and M.S. power engineering courses. After a brief summary of power generating models considered for the bids formulation, the article illustrates the capabilities and main features of OPTIOFER using two simple hydraulic and thermal power systems as examples. ß