Hexane is shown to undergo isotopic hydrogen exchange with (HCl)-H-2 in supercritical deuterium oxide at 380 and 400 degrees C. The deuteration rate follows pseudo first order kinetics at both temperatures with the methylene reaction rate being about 1.6 times that of methyl. The isotopic exchange reaction is analyzed as a two step acid/base mechanism, with hexane acting as a base analogous to its behavior in ＇magic acid＇ solution. Measured K-b＇s for the methyl group are 3.5 x 10(-28) and 9.2 x 10(-28), while the methylene groups have K-b＇s of 6.0 x 10(-28) and 1.5 x 10(-27) at 380 and 400 degrees C, respectively. No evidence is seen for hydride abstraction, such as formation of carbocation rearrangement species or hydrogen gas evolution as in ＇magic acid＇. Hydride abstraction to form carbocations either does not occur or occurs at a rate too slow to be observed in the time scale of the experiments reported here.