Communication: Mercury is emitted into the environment by various anthropogenic and natural activities. Hg reacts with Cl-2 even at ambient temperature. While this reaction is a subject of great interest, data for this system is scarce, apparently due to experimental difficulties. In this work, the reported data for the reaction between Hg and Cl-2 is reanalyzed, and possible mechanisms and environmental effects are discussed. The results strongly support the hypothesis that the reaction of Hg and Cl-2 is a surface reaction, which takes place at the reactor wall.