Economics and stability are two disjoint areas of power system operation that also require different parameters. Fundamental factors in the economic operation are combinatorial explosiveness, distributed nature of the system, and dominance of the human factors. A case where human factor is evidently dominant is due to the recent trend in thermal power stations to use natural gas from multiple gas fields to ensure reliability of service. Fuel cost characteristics change without knowledge of central dispatch office when the plant engineer shift the units from one fuel to the other. A mathematical model and an algorithm have been developed for online computation of these characteristics. Some elements in the economic dispatch of these units may take advantage from Coupled Expert Systems. This paper discusses some of the issues that arise in the economic dispatch of these units and a prospective coupled knowledge-based model has been presented.