We determined the influence of a Pt/C catalyst, high-pressure H(2), and pH on the upgrading of a crude algal bio-oil in supercritical water (SCW). The SCW treatment led to a product oil with a higher heating value (similar to 42 MJ/kg) and lower acid number than the crude bio-oil. The product oil was also lower in 0 and N and essentially free of sulfur. Including the Pt/C catalyst in the reactor led to a freely flowing liquid product oil with a high abundance of hydrocarbons. Overall, many of the properties of the upgraded oil obtained from catalytic treatment in SCW are similar to those of hydrocarbon fuels derived from fossil fuel resources. Thus, this work shows that the crude bio-oil from hydrothermal liquefaction of a microalga can be effectively upgraded in supercritical water in the presence of a Pt/C catalyst. (C) 2010 Elsevier Ltd. All rights reserved.