Thermodynamic analyses of different proposed reaction pathways to determine the thermodynamic feasibility of FT reactions on a mono- and diatomic Ru-complex as model catalysts were performed. Ru(CO)(5) and Ru-2(CO)(g) were taken as starting complexes. The calculations illustrate that a minimum of two adjacent metal atoms is required for C-O bond cleavage and chain growth in the Fischer-Tropsch synthesis. The CO-insertion mechanism seems to be thermodynamically most feasible reaction pathway on diatomic Ru-clusters. (C) 2008 Elsevier B.V. All rights reserved.