The reaction progress in supercritical water oxidation (SCWO) of methanol is simulated in terms of a detailed chemical kinetics model for the two ideal reactors, plug flow reactor (PFR) and continuous stirred tank reactor (CSTR). The reaction has an induction time and a character of first order reaction against the methanol concentration in PFR. The reaction does not appreciably depend on the oxygen concentration as far as the methanol conversion is concerned. In CSTR, the dependence of methanol conversion X on residence time t can be described using a simple first order relation applicable to CSTR, taking into account the induction time tau phenomenologically, that is, X/(1 - X) = k(t - tau). Conversion in the CSTR increases very rapidly against the residence time, compared with that in the PFR, and correspondingly the induction time is much shorter. The dependence of concentrations of intermediates, i.e., CH2O and CO, against the residence time in CSTR is weaker than that in PFR, which is also the case for radical species, in particular, HO2 and OH. Relevant elementary reactions are discussed.