A study was performed at the Energy and Environmental Research Center (EERC) to test the hypotheses that (1) different carbon types contained in coal combustion fly ash have variable sorption capabilities relative to mercury and (2) the inorganic fraction of coal combustion fly ash may sorb mercury through mechanisms distinct from sorption by carbon in the ash. The purpose of this study was to conduct laboratory experiments to better understand the phenomenon of mercury sorption on coal combustion fly ash. Tests were conducted on the laboratory scale using samples generated from both commercial-scale utility boilers and pilot-scale combustion equipment at the EERC. Selected samples represented ash from various coal sources, of varying loss-on-ignition (LOI) content, and exhibiting different combinations of carbon types. Results indicate a direct correlation between carbon content and mercury partitioning among individual ash samples. The direct relationship between carbon content and mercury-sorbing capacity of the bulk ash samples demonstrated in the loading experiments is not reflected by the low- and high-carbon fraction data. The mercury-sorbing capacity of the inorganic fraction is extremely low with respect to carbon present in the ash. There are likely to be significant differences between the mercury-sorbing capacities of these various carbon forms. The mercury-sorbing capacity of ash studied in this research was highly temperature dependent. Additional work is needed on experimental design to evaluate the loading of high-carbon ash samples with particular attention to the phenomenon of sorptive capacity regeneration, which should be further investigated.