The catalytic partial oxidation of n-decane and n-hexadecane with air over a Rh-coated monolith produces synthesis gas (H-2 and CO) in selectivities exceeding 80%, with > 99% conversion of fuels and 100% conversion of oxygen at catalyst contact times from 5 to 25 ms. The high boiling hydrocarbons were delivered as liquids using an automotive fuel injector into a heated chamber where they vaporized in the presence of air. This system creates temperature and concentration gradients that allow safe mixing of fuel with air at temperatures above the autoignition of the fuel. Fuel-rich feeds beyond the syngas ratio produced olefins with selectivities as high as 80% in the case of n-hexadecane. The distribution of these olefins goes from primarily ethylene to large alpha-olefins as oxygen feed is decreased. Partial oxidation of low sulfur diesel fuel was also carried out successfully, producing synthesis gas at > 98% fuel conversion with several hours of stable operation. (C) 2003 Published by Elsevier Science (USA).