A number of environmental strategies in compliance with the provisions of the Framework Convention on Climate Change (FCCC) are currently being analyzed by utilities. Natural gas is often the most important one, since its use emits carbon dioxide (CO2) far less than other fossil fuels. The use of natural gas is therefore under serious consideration as a strategy to reduce the impact on global warming from coal thermal plants under current technological levels. In this article, a cost minimization model is formulated to investigate the feasibility for this strategy from a long-term economic viewpoint. The model developed is comprised of various strategies such as installing scrubbers, purchasing emission credits, or switching fuels for fossil plants, especially coal-fired thermals, which are currently being implemented or considered by utilities. The implemented results show that substitution of natural gas is less economical than other strategies.