The hydrothermal upgrading of pyrolysis oil derived from European spruce has been studied at near and supercritical conditions. (31)p NMR was used to monitor the compositional changes of organic hydroxy oxygenates from upgrading of the pyrolysis oil. The aliphatic OH are shown to be highly reactive undergoing deoxygenation at short reaction times at 383 degrees C. Comparison of (31)p NMR with CHN elemental analysis showed that loss of aliphatic OH was the main deoxygenation process at the conditions used. The hydrothermal upgrading of a four-component, model oil was also studied at similar conditions, where the main products were characterised by GC-MS. (C) 2013 Elsevier Ltd. All rights reserved.