A microwave (2.45 GHz) "tornado"-type plasma with a high-speed tangential gas injection (swirl) at atmospheric pressure conditions has been applied for methanol reforming. The vortex gas flow "detaches" the hot plasma core from the wall and stable operation of the plasma source has been achieved. The hydrogen production rate dependence on the partial methanol flux has been investigated both in Ar and Ar + water plasma environments. Hydrogen, carbon oxide and carbon dioxide are the main decomposition products. Mass and FT-IR spectroscopy have been used to detect the species in the outlet gas stream. It has been found that the hydrogen production rate increases by nearly a factor of 1.5 when water is added into the plasma. Higher energetic hydrogen mass yield is achieved when compared with the results obtained under laminar gas flow conditions. Practically 100% methanol conversion rate has been achieved. Moreover, optical emission spectroscopy has been applied to determine the gas temperature, the electron density and the radiative species present in the plasma. A theoretical model based on a set of equations describing the chemical kinetics and the gas thermal balance equation has been developed. The theoretical results on the decomposition products agree well with the experimental ones and confirm that microwave plasma decomposition of methanol is a temperature dependent process. The results clearly show that this type of plasma is an efficient tool for hydrogen production. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.