The present study contributes to the growing understanding of the principal factors governing the release of mercury from coal during combustion and its subsequent adsorption onto coal fly ash. The mercury content of fly ash is, first, dependent on the chemistry of the feed coal(s); if the feed coal Hg content is low, the resulting fly ash Hg content will also be low. In addition, other aspects of the feed coal chemistry, such as the Cl and Br content, contribute to Hg capture by fly ash. With the latter variables, among other aspects of coal quality, accounted for, Hg capture increases with (1) an increase in the amount of fly ash carbon; (2) a decrease in the flue gas temperature; and (3) an increase in the surface area of the fly ash carbon, generally from inertinite through isotropic carbon to anisotropic carbon (for bituminous feed coals).