Dehydration of supercritical t-butanol to yield 2-methyl-propene was observed to occur rapidly and in high yield at elevated pressures without addition of a catalyst. A capillary micro-reactor was used to carry out the reaction at pressures up to 3.1 kbar. The products were characterized in situ using FTIR and NMR and confirmed using GC-MS. The dehydration reaction is proposed to occur by a self-catalyzed Bronsted acid mechanism. An addition driving force for the reaction was the phase separation of the 2-methyl-propene product. Self-catalyzed dehydration of t-butanol is a limiting factor for operations in supercritical t-butanol, but it implies the t-butanol may be employed as a self-neutralizing catalyst under these conditions. (C) 2005 Elsevier B.V. All rights reserved.