Despite the common association between mercury deposits and liquid hydrocarbons, the effects of mercury organic interactions on mercury transport have received little attention. In this study, we estimate the extent of aqueous mercury complexation, and the partitioning of mercury among aqueous liquid, aqueous vapor, and an organic phase, quantifying the relative importance of each phase in mercury transport. The calculations suggest that significant mercury transport in the aqueous liquid, predominantly as Hg 0 (sub (aq)) , is only possible under relatively oxidizing and alkaline conditions. The frequent occurrence of liquid hydrocarbons in mercury-depositing hydrothermal systems, however, implies that conditions are reducing and that aqueous liquid transport of mercury is relatively unimportant. High concentrations of mercury also can be dissolved in aqueous vapor. However, boiling rarely occurs at the depths at which the ore solutions originate, and thus, the presence of a vapor phase is unlikely during mercury transport. Extrapolation of low-temperature experimental measurements of mercury solubilities in organic phases enables quantitative estimates of mercury concentrations in liquid hydrocarbons under hydrothermal conditions. Our calculations suggest that extremely high concentrations of mercury can dissolve in the organic phase and that organic phase transport may control mercury mobilities in many mercury ore-forming hydrothermal systems.