Thin films of Ru and RuO2 were deposited using ruthenocene and oxygen as a precursor and reaction gas, respectively. Two phases, Ru and RuO2, could be deposited using the same source and reaction gas. The phase of the as-deposited film was found to be critically dependent on the deposition process parameters such as precursor partial pressure, oxygen partial pressure, and substrate temperature, A decrease in precursor partial pressure by either reducing carrier gas flow rate or bubbler temperature led to RuO2 formation while a decrease in oxygen partial pressure resulted in Ru formation. It was also identified that there exists a substrate temperature range in which a Ru Film is deposited at a given processing condition. When the temperature is either higher or lower than this temperature range, RuO2 Film deposition results. From careful analysis of the film deposition rate in conjunction with the evolution of the film phase, we conclude that film deposition occurs by two independent processes. One is the source gas decomposition process resulting in Ru him deposition, and the other is the oxidation of the Ru film resulting in RuO2 deposition.