The influence of the addition of 1, 2 or 5 vol.% of CO. H-2 or CO2 to the feed during the partial oxidation of methane (POM) was studied over a Rh/Ti-SiO2 catalyst. The addition of H-2 or CO decreases the conversion and syngas selectivity. This decrease of performance seems to be related to a higher reduction of the catalyst due to the co-feeding of H-2 or CO. The addition of CO2 also appears unfavourable to the production of hydrogen but increases the CO yield. A combination of the dry reforming and the reverse water-gas shift reactions is suggested to explain the observed modifications in the product yields. (C) 2009 Elsevier B.V. All rights reserved.