In a method for optimizing operation of fossil fuel based power plants, in which the economical effects of the changes of selected operational parameters are determined under consideration of the required economical expenditure, and, based on these additional operational costs, it is determined if, when, and/or what kind of measures should be taken for minimizing the additional operational costs. According to the method, the improvement measures are initiated as a function of the cause of the additional operational costs according to a hierarchal catalog of measures. The measures are: an immediate intervention into the operational course; a later measure implemented during a short shutdown; a later measure implemented during a service shutdown; and/or an operational downtime for a revision.