Abstract: The present invention relates to coal-fired power plants and flue gas emissions and more specifically, to controlling gaseous mercury emissions in the flue gas between two or more coal fired electric generating units within a contiguous power plant site to achieve environmental regulation limits for mercury emissions. This is accomplished by continuously adjusting the application rates of mercury oxidant, which is added to a coal feed to oxidize elemental mercury for improved mercury capturability and aqueous mercury precipitant (liquid), which is added to a scrubber liquor of a wet Flue Gas Desulfurization (FGD) unit to precipitate out oxidized mercury into solid form for improved capture and disposal.