This paper investigates the possibilities that exist for switching coal-fired plants to gas-fired plants, depending on load level. A fixed allowance cost and a variable natural gas price are assumed. The method to address greenhouse gas (GHG) emission reduction potentials is first illustrated in a methodological case. Next, the GHG emission reduction potentials are addressed for several western European countries together with a relative positioning of their electricity generation. GHG emission reduction potentials are also compared with simulation results.