This paper presents thermodynamic analysis of hydrogen production by partial oxidation reforming. The analysis applies two approximations to the chemistry: global reaction balances and chemical equilibrium. The global reaction analysis provides theoretical upper limits on the process in the form of algebraic expressions involving the steam-to-carbon ratio and the oxygen-to-carbon ratio as process parameters. The equilibrium computations provide a more realistic estimate of the expected product composition and thermal efficiency of the process. The equilibrium predictions are compared to experimental data obtained using a first generation plasmatron reformer operated on diesel fuel. The efficiency of this compact reformer was considerably below the theoretical maximum. (C) 2003 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.