We report on the effect of nickel metal on the gasification of methanol in supercritical water at 500 and 550 degrees C. The reactions were conducted in sealed quartz tubes, which allowed the homogeneous and heterogeneous rates to be quantified separately for the first time. In the absence of nickel, conversions up to 20% were reached after 2 h. The pseudo-first-order rate constant for homogeneous gasification is 4.0 +/- 2.7 x 10(-5) s(-1) at 550 degrees C. In the presence of a Ni wire that ran the entire length of the reactor, conversions of up to 90% were reached in less than 5 min. The pseudo-first-order rate constants for Ni-catalyzed gasification are 0.0032 +/- 0.0013 and 0.0040 +/- 0.0012 cm/s at 500 and 550 degrees C. These results show that homogeneous, uncatalyzed gasification in supercritical water is slow, but rates are greatly increased by added Ni. Hydrogen, carbon monoxide and carbon dioxide were the major products detected. Hydrogen was always the most abundant. With multiple uses, the Ni wire showed deactivation as a catalyst for methanol gasification. (c) 2006 Elsevier B.V.. All rights reserved.