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 Rh/Ti-modified support catalysts (Rh/Ti-SiO2. Rh/Ti-Al2O3 and Rh/Ti-MgO). The changes observed in the conversion and syngas selectivity in the presence of gaseous co-feeds are due to changes in the kinetics of POM and may be mainly explained by modifications in the oxidation state of rhodium during the reaction. A higher reduction of Rh is observed when 5% of H-2 or CO is co-fed while Rh is maintained in a higher oxidation state in the presence of CO2 co-feed. Reversibility tests show that the modifications induced by the gaseous promoters in the catalytic performances are reversible. Such changes can alter not only the kinetics of POM but also the kinetics of the other reactions involved (dry reforming and the reverse water-gas shift) during POM reaction. Results have implications in the expression of the reaction kinetics to be used in the modelling of POM reaction mechanism. (C) 2011 Elsevier B.V. All rights reserved.