Density functional theory of bond dissociation energies of the metal-ligand bonds, thermodynamic investigation of the stability of intermediate species, and experimental investigation of the composition of the gas phase by on-line mass spectrometry have been performed in order to study the growth mechanisms and the carbon incorporation in nickel films during metallorganic chemical vapor deposition (MOCVD) of nickel from nickelocene. A model is proposed, according to which nickelocene molecules are adsorbed on the surface. Cyclopentadiene is formed from the reaction between two cyclopentadienyl ligands of neighboring molecules, while hydrogen-deficient C-5 rings serve as starting species for carbon incorporation in the films via subsequent dehydrogenation. The hydrogen atoms available react with nickel cyclopentadienyl radicals to form hydrogenated intermediate species which are desorbed from the surface. This model is compatible with the data from the literature on the different steps of the decomposition process.